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 $213.46   9.741%   $234.2531   $234.25   $234.25   $234.30  
  Purchase #2 $199.26   4.380%   $207.9876   $207.99   $208.00   $208.00  
  Purchase #3 $240.25   7.587%   $258.4778   $258.48   $258.50   $258.50  
  Purchase #4 $226.39   8.112%   $244.7548   $244.75   $244.75   $244.80  
  Purchase #5 $165.29   3.774%   $171.528   $171.53   $171.55   $171.50  
  Purchase #6 $182.31   10.815%   $202.0268   $202.03   $202.05   $202.00  
  Purchase #7 $27.94   5.672%   $29.5248   $29.52   $29.50   $29.50  
  7 purchase totals = $1,254.90       $1,348.5529   $1,348.55   $1,348.60   $1,348.60