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 $68.86   13.592%   $78.2195   $78.22   $78.20   $78.20  
  Purchase #2 $68.59   3.668%   $71.1059   $71.11   $71.10   $71.10  
  Purchase #3 $24.26   10.190%   $26.7321   $26.73   $26.75   $26.70  
  Purchase #4 $218.93   13.359%   $248.1769   $248.18   $248.20   $248.20  
  Purchase #5 $213.65   4.601%   $223.48   $223.48   $223.50   $223.50  
  Purchase #6 $201.38   8.464%   $218.4248   $218.42   $218.40   $218.40  
  Purchase #7 $201.59   13.494%   $228.7926   $228.79   $228.80   $228.80  
  7 purchase totals = $997.26       $1,094.9318   $1,094.93   $1,094.95   $1,094.90