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 $240.72   13.591%   $273.4363   $273.44   $273.45   $273.40  
  Purchase #2 $85.50   6.644%   $91.1806   $91.18   $91.20   $91.20  
  Purchase #3 $98.89   4.504%   $103.344   $103.34   $103.35   $103.30  
  Purchase #4 $211.47   11.357%   $235.4866   $235.49   $235.50   $235.50  
  Purchase #5 $153.45   4.465%   $160.3015   $160.30   $160.30   $160.30  
  Purchase #6 $171.52   8.806%   $186.6241   $186.62   $186.60   $186.60  
  Purchase #7 $79.37   6.774%   $84.7465   $84.75   $84.75   $84.70  
  7 purchase totals = $1,040.92       $1,135.1196   $1,135.12   $1,135.15   $1,135.00