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 $58.73   5.612%   $62.0259   $62.03   $62.05   $62.00  
  Purchase #2 $81.87   11.817%   $91.5446   $91.54   $91.55   $91.50  
  Purchase #3 $205.97   10.594%   $227.7905   $227.79   $227.80   $227.80  
  Purchase #4 $36.35   11.110%   $40.3885   $40.39   $40.40   $40.40  
  Purchase #5 $162.97   8.643%   $177.0555   $177.06   $177.05   $177.10  
  Purchase #6 $181.51   7.668%   $195.4282   $195.43   $195.45   $195.40  
  Purchase #7 $60.53   10.496%   $66.8832   $66.88   $66.90   $66.90  
  7 purchase totals = $787.93       $861.1164   $861.12   $861.20   $861.10