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 $56.98   6.648%   $60.768   $60.77   $60.75   $60.80  
  Purchase #2 $59.34   12.223%   $66.5931   $66.59   $66.60   $66.60  
  Purchase #3 $215.46   6.746%   $229.9949   $229.99   $230.00   $230.00  
  Purchase #4 $174.25   6.590%   $185.7331   $185.73   $185.75   $185.70  
  Purchase #5 $221.78   13.569%   $251.8733   $251.87   $251.85   $251.90  
  Purchase #6 $108.47   11.144%   $120.5579   $120.56   $120.55   $120.60  
  Purchase #7 $24.47   4.612%   $25.5986   $25.60   $25.60   $25.60  
  7 purchase totals = $860.75       $941.1189   $941.11   $941.10   $941.20