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 $223.39   13.713%   $254.0235   $254.02   $254.00   $254.00  
  Purchase #2 $29.78   6.173%   $31.6183   $31.62   $31.60   $31.60  
  Purchase #3 $156.51   13.495%   $177.631   $177.63   $177.65   $177.60  
  Purchase #4 $207.65   12.149%   $232.8774   $232.88   $232.90   $232.90  
  Purchase #5 $143.87   7.251%   $154.302   $154.30   $154.30   $154.30  
  Purchase #6 $221.62   12.719%   $249.8078   $249.81   $249.80   $249.80  
  Purchase #7 $44.46   4.455%   $46.4407   $46.44   $46.45   $46.40  
  7 purchase totals = $1,027.28       $1,146.7007   $1,146.70   $1,146.70   $1,146.60