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 $33.50   9.371%   $36.6393   $36.64   $36.65   $36.60  
  Purchase #2 $224.39   9.703%   $246.1626   $246.16   $246.15   $246.20  
  Purchase #3 $203.93   6.389%   $216.9591   $216.96   $216.95   $217.00  
  Purchase #4 $220.72   6.268%   $234.5547   $234.55   $234.55   $234.60  
  Purchase #5 $93.83   9.828%   $103.0516   $103.05   $103.05   $103.10  
  Purchase #6 $45.56   5.630%   $48.125   $48.13   $48.15   $48.10  
  Purchase #7 $48.51   6.314%   $51.5729   $51.57   $51.55   $51.60  
  7 purchase totals = $870.44       $937.0652   $937.06   $937.05   $937.20