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 $62.66   11.679%   $69.9781   $69.98   $70.00   $70.00  
  Purchase #2 $238.43   12.595%   $268.4603   $268.46   $268.45   $268.50  
  Purchase #3 $111.71   10.507%   $123.4474   $123.45   $123.45   $123.40  
  Purchase #4 $169.48   8.686%   $184.201   $184.20   $184.20   $184.20  
  Purchase #5 $215.78   13.190%   $244.2414   $244.24   $244.25   $244.20  
  Purchase #6 $5.31   11.351%   $5.9127   $5.91   $5.90   $5.90  
  Purchase #7 $6.53   7.804%   $7.0396   $7.04   $7.05   $7.00  
  7 purchase totals = $809.90       $903.2805   $903.28   $903.30   $903.20