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 $162.92   12.498%   $183.2817   $183.28   $183.30   $183.30  
  Purchase #2 $101.72   10.425%   $112.3243   $112.32   $112.30   $112.30  
  Purchase #3 $66.41   12.169%   $74.4914   $74.49   $74.50   $74.50  
  Purchase #4 $203.68   6.706%   $217.3388   $217.34   $217.35   $217.30  
  Purchase #5 $88.88   3.112%   $91.6459   $91.65   $91.65   $91.60  
  Purchase #6 $62.52   9.222%   $68.2856   $68.29   $68.30   $68.30  
  Purchase #7 $169.83   4.847%   $178.0617   $178.06   $178.05   $178.10  
  7 purchase totals = $855.96       $925.4294   $925.43   $925.45   $925.40