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 $83.56   12.774%   $94.234   $94.23   $94.25   $94.20  
  Purchase #2 $227.52   9.662%   $249.503   $249.50   $249.50   $249.50  
  Purchase #3 $31.26   4.833%   $32.7708   $32.77   $32.75   $32.80  
  Purchase #4 $145.86   12.585%   $164.2165   $164.22   $164.20   $164.20  
  Purchase #5 $155.93   7.496%   $167.6185   $167.62   $167.60   $167.60  
  Purchase #6 $130.60   12.814%   $147.3351   $147.34   $147.35   $147.30  
  Purchase #7 $100.65   12.173%   $112.9021   $112.90   $112.90   $112.90  
  7 purchase totals = $875.38       $968.5800   $968.58   $968.55   $968.50