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 $57.94   12.776%   $65.3424   $65.34   $65.35   $65.30  
  Purchase #2 $176.51   7.762%   $190.2107   $190.21   $190.20   $190.20  
  Purchase #3 $232.73   9.777%   $255.484   $255.48   $255.50   $255.50  
  Purchase #4 $246.95   8.770%   $268.6075   $268.61   $268.60   $268.60  
  Purchase #5 $59.46   10.678%   $65.8091   $65.81   $65.80   $65.80  
  Purchase #6 $188.59   4.525%   $197.1237   $197.12   $197.10   $197.10  
  Purchase #7 $243.64   9.173%   $265.9891   $265.99   $266.00   $266.00  
  7 purchase totals = $1,205.82       $1,308.5665   $1,308.56   $1,308.55   $1,308.50