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 $11.27   4.711%   $11.8009   $11.80   $11.80   $11.80  
  Purchase #2 $119.74   4.777%   $125.46   $125.46   $125.45   $125.50  
  Purchase #3 $67.29   8.172%   $72.7889   $72.79   $72.80   $72.80  
  Purchase #4 $94.27   13.350%   $106.855   $106.86   $106.85   $106.90  
  Purchase #5 $181.96   9.539%   $199.3172   $199.32   $199.30   $199.30  
  Purchase #6 $105.59   12.279%   $118.5554   $118.56   $118.55   $118.60  
  Purchase #7 $125.85   11.630%   $140.4864   $140.49   $140.50   $140.50  
  7 purchase totals = $705.97       $775.2638   $775.28   $775.25   $775.40