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 $236.92   7.745%   $255.2695   $255.27   $255.25   $255.30  
  Purchase #2 $45.53   9.341%   $49.783   $49.78   $49.80   $49.80  
  Purchase #3 $41.32   11.308%   $45.9925   $45.99   $46.00   $46.00  
  Purchase #4 $202.33   9.570%   $221.693   $221.69   $221.70   $221.70  
  Purchase #5 $61.57   12.199%   $69.0809   $69.08   $69.10   $69.10  
  Purchase #6 $149.49   5.300%   $157.413   $157.41   $157.40   $157.40  
  Purchase #7 $225.71   10.484%   $249.3734   $249.37   $249.35   $249.40  
  7 purchase totals = $962.87       $1,048.6053   $1,048.59   $1,048.60   $1,048.70