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 $57.98   10.326%   $63.967   $63.97   $63.95   $64.00  
  Purchase #2 $132.78   12.114%   $148.865   $148.87   $148.85   $148.90  
  Purchase #3 $100.35   10.161%   $110.5466   $110.55   $110.55   $110.50  
  Purchase #4 $65.84   5.478%   $69.4467   $69.45   $69.45   $69.40  
  Purchase #5 $231.74   7.182%   $248.3836   $248.38   $248.40   $248.40  
  Purchase #6 $185.26   9.858%   $203.5229   $203.52   $203.50   $203.50  
  Purchase #7 $189.35   6.735%   $202.1027   $202.10   $202.10   $202.10  
  7 purchase totals = $963.30       $1,046.8345   $1,046.84   $1,046.80   $1,046.80