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 $77.31   10.662%   $85.5528   $85.55   $85.55   $85.60  
  Purchase #2 $183.71   7.779%   $198.0008   $198.00   $198.00   $198.00  
  Purchase #3 $39.50   10.873%   $43.7948   $43.79   $43.80   $43.80  
  Purchase #4 $97.87   8.766%   $106.4493   $106.45   $106.45   $106.40  
  Purchase #5 $32.55   8.203%   $35.2201   $35.22   $35.20   $35.20  
  Purchase #6 $248.84   10.549%   $275.0901   $275.09   $275.10   $275.10  
  Purchase #7 $46.33   3.476%   $47.9404   $47.94   $47.95   $47.90  
  7 purchase totals = $726.11       $792.0483   $792.04   $792.05   $792.00