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 $51.98   13.111%   $58.7951   $58.80   $58.80   $58.80  
  Purchase #2 $195.64   6.511%   $208.3781   $208.38   $208.40   $208.40  
  Purchase #3 $245.32   10.497%   $271.0712   $271.07   $271.05   $271.10  
  Purchase #4 $156.88   6.781%   $167.518   $167.52   $167.50   $167.50  
  Purchase #5 $140.33   5.130%   $147.5289   $147.53   $147.55   $147.50  
  Purchase #6 $87.78   8.170%   $94.9516   $94.95   $94.95   $95.00  
  Purchase #7 $215.51   5.621%   $227.6238   $227.62   $227.60   $227.60  
  7 purchase totals = $1,093.44       $1,175.8667   $1,175.87   $1,175.85   $1,175.90