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 $54.93   12.653%   $61.8803   $61.88   $61.90   $61.90  
  Purchase #2 $238.74   9.233%   $260.7829   $260.78   $260.80   $260.80  
  Purchase #3 $55.85   13.795%   $63.5545   $63.55   $63.55   $63.60  
  Purchase #4 $231.39   3.580%   $239.6738   $239.67   $239.65   $239.70  
  Purchase #5 $238.25   11.226%   $264.9959   $265.00   $265.00   $265.00  
  Purchase #6 $181.97   9.560%   $199.3663   $199.37   $199.35   $199.40  
  Purchase #7 $246.49   13.647%   $280.1285   $280.13   $280.15   $280.10  
  7 purchase totals = $1,247.62       $1,370.3822   $1,370.38   $1,370.40   $1,370.50