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 $61.80   8.363%   $66.9683   $66.97   $66.95   $67.00  
  Purchase #2 $115.61   11.585%   $129.0034   $129.00   $129.00   $129.00  
  Purchase #3 $115.74   13.745%   $131.6485   $131.65   $131.65   $131.60  
  Purchase #4 $243.46   13.130%   $275.4263   $275.43   $275.45   $275.40  
  Purchase #5 $69.78   8.630%   $75.802   $75.80   $75.80   $75.80  
  Purchase #6 $149.69   10.600%   $165.5571   $165.56   $165.55   $165.60  
  Purchase #7 $221.43   13.597%   $251.5378   $251.54   $251.55   $251.50  
  7 purchase totals = $977.51       $1,095.9434   $1,095.95   $1,095.95   $1,095.90