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 $88.50   4.171%   $92.1913   $92.19   $92.20   $92.20  
  Purchase #2 $217.40   11.199%   $241.7466   $241.75   $241.75   $241.70  
  Purchase #3 $86.76   6.592%   $92.4792   $92.48   $92.50   $92.50  
  Purchase #4 $30.26   6.465%   $32.2163   $32.22   $32.20   $32.20  
  Purchase #5 $124.92   9.293%   $136.5288   $136.53   $136.55   $136.50  
  Purchase #6 $51.77   3.728%   $53.7   $53.70   $53.70   $53.70  
  Purchase #7 $190.67   5.524%   $201.2026   $201.20   $201.20   $201.20  
  7 purchase totals = $790.28       $850.0648   $850.07   $850.10   $850.00