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 $221.37   13.624%   $251.5294   $251.53   $251.55   $251.50  
  Purchase #2 $53.57   13.455%   $60.7778   $60.78   $60.80   $60.80  
  Purchase #3 $246.45   7.803%   $265.6805   $265.68   $265.70   $265.70  
  Purchase #4 $246.64   4.613%   $258.0175   $258.02   $258.00   $258.00  
  Purchase #5 $84.45   8.351%   $91.5024   $91.50   $91.50   $91.50  
  Purchase #6 $65.39   13.519%   $74.2301   $74.23   $74.25   $74.20  
  Purchase #7 $114.75   9.144%   $125.2427   $125.24   $125.25   $125.20  
  7 purchase totals = $1,032.62       $1,126.9804   $1,126.98   $1,127.05   $1,126.90