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 $92.97   9.276%   $101.5939   $101.59   $101.60   $101.60  
  Purchase #2 $177.33   9.553%   $194.2703   $194.27   $194.25   $194.30  
  Purchase #3 $27.42   11.103%   $30.4644   $30.46   $30.45   $30.50  
  Purchase #4 $71.95   5.294%   $75.759   $75.76   $75.75   $75.80  
  Purchase #5 $54.30   5.348%   $57.204   $57.20   $57.20   $57.20  
  Purchase #6 $13.52   9.780%   $14.8423   $14.84   $14.85   $14.80  
  Purchase #7 $247.40   8.499%   $268.4265   $268.43   $268.45   $268.40  
  7 purchase totals = $684.89       $742.5604   $742.55   $742.55   $742.60