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 $58.51   8.273%   $63.3505   $63.35   $63.35   $63.40  
  Purchase #2 $26.37   11.224%   $29.3298   $29.33   $29.35   $29.30  
  Purchase #3 $121.34   9.579%   $132.9632   $132.96   $132.95   $133.00  
  Purchase #4 $235.32   11.385%   $262.1112   $262.11   $262.10   $262.10  
  Purchase #5 $181.96   13.804%   $207.0778   $207.08   $207.10   $207.10  
  Purchase #6 $131.28   10.183%   $144.6482   $144.65   $144.65   $144.60  
  Purchase #7 $177.49   9.686%   $194.6817   $194.68   $194.70   $194.70  
  7 purchase totals = $932.27       $1,034.1624   $1,034.16   $1,034.20   $1,034.20