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 $67.25   9.424%   $73.5876   $73.59   $73.60   $73.60  
  Purchase #2 $113.37   4.688%   $118.6848   $118.68   $118.70   $118.70  
  Purchase #3 $173.98   12.383%   $195.5239   $195.52   $195.50   $195.50  
  Purchase #4 $69.62   11.735%   $77.7899   $77.79   $77.80   $77.80  
  Purchase #5 $207.47   5.234%   $218.329   $218.33   $218.35   $218.30  
  Purchase #6 $90.71   12.159%   $101.7394   $101.74   $101.75   $101.70  
  Purchase #7 $215.29   10.781%   $238.5004   $238.50   $238.50   $238.50  
  7 purchase totals = $937.69       $1,024.1550   $1,024.15   $1,024.20   $1,024.10