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 $59.98   5.171%   $63.0816   $63.08   $63.10   $63.10  
  Purchase #2 $59.70   7.163%   $63.9763   $63.98   $64.00   $64.00  
  Purchase #3 $238.98   12.700%   $269.3305   $269.33   $269.35   $269.30  
  Purchase #4 $37.85   7.343%   $40.6293   $40.63   $40.65   $40.60  
  Purchase #5 $197.85   8.694%   $215.0511   $215.05   $215.05   $215.10  
  Purchase #6 $11.93   12.344%   $13.4026   $13.40   $13.40   $13.40  
  Purchase #7 $230.97   7.812%   $249.0134   $249.01   $249.00   $249.00  
  7 purchase totals = $837.26       $914.4848   $914.48   $914.55   $914.50