Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.86   9.811%   $224.9588   $224.96   $224.95   $225.00  
  Purchase #2 $187.84   10.268%   $207.1274   $207.13   $207.15   $207.10  
  Purchase #3 $96.68   12.351%   $108.6209   $108.62   $108.60   $108.60  
  Purchase #4 $151.84   3.691%   $157.4444   $157.44   $157.45   $157.40  
  Purchase #5 $211.43   6.740%   $225.6804   $225.68   $225.70   $225.70  
  Purchase #6 $196.35   5.176%   $206.5131   $206.51   $206.50   $206.50  
  Purchase #7 $207.35   9.824%   $227.7201   $227.72   $227.70   $227.70  
  7 purchase totals = $1,256.35       $1,358.0651   $1,358.06   $1,358.05   $1,358.00