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 $235.98   10.572%   $260.9278   $260.93   $260.95   $260.90  
  Purchase #2 $197.37   3.866%   $205.0003   $205.00   $205.00   $205.00  
  Purchase #3 $126.48   3.584%   $131.013   $131.01   $131.00   $131.00  
  Purchase #4 $38.38   3.446%   $39.7026   $39.70   $39.70   $39.70  
  Purchase #5 $157.36   7.410%   $169.0204   $169.02   $169.00   $169.00  
  Purchase #6 $53.29   13.605%   $60.5401   $60.54   $60.55   $60.50  
  Purchase #7 $204.80   11.204%   $227.7458   $227.75   $227.75   $227.70  
  7 purchase totals = $1,013.66       $1,093.9500   $1,093.95   $1,093.95   $1,093.80