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 $233.30   13.581%   $264.9845   $264.98   $265.00   $265.00  
  Purchase #2 $26.85   9.245%   $29.3323   $29.33   $29.35   $29.30  
  Purchase #3 $49.92   11.117%   $55.4696   $55.47   $55.45   $55.50  
  Purchase #4 $135.72   7.421%   $145.7918   $145.79   $145.80   $145.80  
  Purchase #5 $29.42   7.266%   $31.5577   $31.56   $31.55   $31.60  
  Purchase #6 $208.76   13.227%   $236.3727   $236.37   $236.35   $236.40  
  Purchase #7 $191.73   5.638%   $202.5397   $202.54   $202.55   $202.50  
  7 purchase totals = $875.70       $966.0483   $966.04   $966.05   $966.10