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 $59.62   3.221%   $61.5404   $61.54   $61.55   $61.50  
  Purchase #2 $222.66   11.736%   $248.7914   $248.79   $248.80   $248.80  
  Purchase #3 $58.47   6.351%   $62.1834   $62.18   $62.20   $62.20  
  Purchase #4 $218.79   6.207%   $232.3703   $232.37   $232.35   $232.40  
  Purchase #5 $42.40   5.136%   $44.5777   $44.58   $44.60   $44.60  
  Purchase #6 $155.95   9.737%   $171.1349   $171.13   $171.15   $171.10  
  Purchase #7 $59.62   11.327%   $66.3732   $66.37   $66.35   $66.40  
  7 purchase totals = $817.51       $886.9713   $886.96   $887.00   $887.00