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 $203.62   10.497%   $224.994   $224.99   $225.00   $225.00  
  Purchase #2 $74.88   6.783%   $79.9591   $79.96   $79.95   $80.00  
  Purchase #3 $22.56   9.620%   $24.7303   $24.73   $24.75   $24.70  
  Purchase #4 $89.28   10.596%   $98.7401   $98.74   $98.75   $98.70  
  Purchase #5 $244.83   4.810%   $256.6063   $256.61   $256.60   $256.60  
  Purchase #6 $209.84   11.321%   $233.596   $233.60   $233.60   $233.60  
  Purchase #7 $188.52   10.371%   $208.0714   $208.07   $208.05   $208.10  
  7 purchase totals = $1,033.53       $1,126.6972   $1,126.70   $1,126.70   $1,126.70