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 $178.97   8.392%   $193.9892   $193.99   $194.00   $194.00  
  Purchase #2 $21.82   13.303%   $24.7227   $24.72   $24.70   $24.70  
  Purchase #3 $155.94   13.519%   $177.0215   $177.02   $177.00   $177.00  
  Purchase #4 $177.60   13.767%   $202.0502   $202.05   $202.05   $202.10  
  Purchase #5 $152.43   8.348%   $165.1549   $165.15   $165.15   $165.20  
  Purchase #6 $104.85   6.495%   $111.66   $111.66   $111.65   $111.70  
  Purchase #7 $67.95   12.130%   $76.1923   $76.19   $76.20   $76.20  
  7 purchase totals = $859.56       $950.7908   $950.78   $950.75   $950.90