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 $64.59   8.757%   $70.2461   $70.25   $70.25   $70.20  
  Purchase #2 $95.55   7.201%   $102.4306   $102.43   $102.45   $102.40  
  Purchase #3 $228.86   13.245%   $259.1725   $259.17   $259.15   $259.20  
  Purchase #4 $197.38   10.315%   $217.7397   $217.74   $217.75   $217.70  
  Purchase #5 $143.45   7.376%   $154.0309   $154.03   $154.05   $154.00  
  Purchase #6 $205.67   3.550%   $212.9713   $212.97   $212.95   $213.00  
  Purchase #7 $37.95   8.861%   $41.3127   $41.31   $41.30   $41.30  
  7 purchase totals = $973.45       $1,057.9038   $1,057.90   $1,057.90   $1,057.80