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 $246.33   6.439%   $262.1912   $262.19   $262.20   $262.20  
  Purchase #2 $111.77   6.512%   $119.0485   $119.05   $119.05   $119.00  
  Purchase #3 $150.71   11.445%   $167.9588   $167.96   $167.95   $168.00  
  Purchase #4 $178.40   9.253%   $194.9074   $194.91   $194.90   $194.90  
  Purchase #5 $88.92   4.122%   $92.5853   $92.59   $92.60   $92.60  
  Purchase #6 $70.27   7.228%   $75.3491   $75.35   $75.35   $75.30  
  Purchase #7 $184.54   13.497%   $209.4474   $209.45   $209.45   $209.40  
  7 purchase totals = $1,030.94       $1,121.4877   $1,121.50   $1,121.50   $1,121.40