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 $153.84   8.464%   $166.861   $166.86   $166.85   $166.90  
  Purchase #2 $228.99   9.409%   $250.5357   $250.54   $250.55   $250.50  
  Purchase #3 $45.53   10.131%   $50.1426   $50.14   $50.15   $50.10  
  Purchase #4 $161.67   13.349%   $183.2513   $183.25   $183.25   $183.30  
  Purchase #5 $10.94   9.538%   $11.9835   $11.98   $12.00   $12.00  
  Purchase #6 $24.45   4.382%   $25.5214   $25.52   $25.50   $25.50  
  Purchase #7 $227.48   5.717%   $240.485   $240.49   $240.50   $240.50  
  7 purchase totals = $852.90       $928.7805   $928.78   $928.80   $928.80