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 $68.65   13.586%   $77.9768   $77.98   $78.00   $78.00  
  Purchase #2 $158.79   5.606%   $167.6918   $167.69   $167.70   $167.70  
  Purchase #3 $79.48   4.360%   $82.9453   $82.95   $82.95   $82.90  
  Purchase #4 $92.46   13.197%   $104.6619   $104.66   $104.65   $104.70  
  Purchase #5 $171.78   12.644%   $193.4999   $193.50   $193.50   $193.50  
  Purchase #6 $143.91   10.835%   $159.5026   $159.50   $159.50   $159.50  
  Purchase #7 $187.59   5.281%   $197.4966   $197.50   $197.50   $197.50  
  7 purchase totals = $902.66       $983.7749   $983.78   $983.80   $983.80