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 $78.49   8.715%   $85.3304   $85.33   $85.35   $85.30  
  Purchase #2 $155.48   12.424%   $174.7968   $174.80   $174.80   $174.80  
  Purchase #3 $88.90   4.787%   $93.1556   $93.16   $93.15   $93.20  
  Purchase #4 $95.25   3.563%   $98.6438   $98.64   $98.65   $98.60  
  Purchase #5 $218.31   3.157%   $225.202   $225.20   $225.20   $225.20  
  Purchase #6 $137.94   12.495%   $155.1756   $155.18   $155.20   $155.20  
  Purchase #7 $213.48   9.277%   $233.2845   $233.28   $233.30   $233.30  
  7 purchase totals = $987.85       $1,065.5887   $1,065.59   $1,065.65   $1,065.60