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 $207.82   11.671%   $232.0747   $232.07   $232.05   $232.10  
  Purchase #2 $57.91   5.674%   $61.1958   $61.20   $61.20   $61.20  
  Purchase #3 $182.33   11.562%   $203.411   $203.41   $203.40   $203.40  
  Purchase #4 $22.58   5.464%   $23.8138   $23.81   $23.80   $23.80  
  Purchase #5 $106.43   10.243%   $117.3316   $117.33   $117.35   $117.30  
  Purchase #6 $140.72   6.736%   $150.1989   $150.20   $150.20   $150.20  
  Purchase #7 $221.84   11.135%   $246.5419   $246.54   $246.55   $246.50  
  7 purchase totals = $939.63       $1,034.5677   $1,034.56   $1,034.55   $1,034.50