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 $170.79   13.123%   $193.2028   $193.20   $193.20   $193.20  
  Purchase #2 $232.57   11.748%   $259.8923   $259.89   $259.90   $259.90  
  Purchase #3 $50.97   10.557%   $56.3509   $56.35   $56.35   $56.40  
  Purchase #4 $103.56   4.178%   $107.8867   $107.89   $107.90   $107.90  
  Purchase #5 $207.77   13.487%   $235.7919   $235.79   $235.80   $235.80  
  Purchase #6 $194.38   6.201%   $206.4335   $206.43   $206.45   $206.40  
  Purchase #7 $136.46   5.353%   $143.7647   $143.76   $143.75   $143.80  
  7 purchase totals = $1,096.50       $1,203.3228   $1,203.31   $1,203.35   $1,203.40