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 $247.56   11.703%   $276.5319   $276.53   $276.55   $276.50  
  Purchase #2 $25.78   7.713%   $27.7684   $27.77   $27.75   $27.80  
  Purchase #3 $177.90   7.854%   $191.8723   $191.87   $191.85   $191.90  
  Purchase #4 $221.93   5.830%   $234.8685   $234.87   $234.85   $234.90  
  Purchase #5 $48.49   7.788%   $52.2664   $52.27   $52.25   $52.30  
  Purchase #6 $16.62   13.591%   $18.8788   $18.88   $18.90   $18.90  
  Purchase #7 $218.40   3.244%   $225.4849   $225.48   $225.50   $225.50  
  7 purchase totals = $956.68       $1,027.6712   $1,027.67   $1,027.65   $1,027.80