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 $188.70   11.762%   $210.8949   $210.89   $210.90   $210.90  
  Purchase #2 $147.58   13.366%   $167.3055   $167.31   $167.30   $167.30  
  Purchase #3 $125.89   12.674%   $141.8453   $141.85   $141.85   $141.80  
  Purchase #4 $49.95   11.398%   $55.6433   $55.64   $55.65   $55.60  
  Purchase #5 $161.40   12.531%   $181.625   $181.63   $181.65   $181.60  
  Purchase #6 $197.89   6.606%   $210.9626   $210.96   $210.95   $211.00  
  Purchase #7 $68.29   10.622%   $75.5438   $75.54   $75.55   $75.50  
  7 purchase totals = $939.70       $1,043.8204   $1,043.82   $1,043.85   $1,043.70