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 $225.68   12.691%   $254.321   $254.32   $254.30   $254.30  
  Purchase #2 $21.86   11.347%   $24.3405   $24.34   $24.35   $24.30  
  Purchase #3 $203.30   8.848%   $221.288   $221.29   $221.30   $221.30  
  Purchase #4 $228.35   3.614%   $236.6026   $236.60   $236.60   $236.60  
  Purchase #5 $238.89   12.410%   $268.5362   $268.54   $268.55   $268.50  
  Purchase #6 $162.26   8.784%   $176.5129   $176.51   $176.50   $176.50  
  Purchase #7 $46.66   12.135%   $52.3222   $52.32   $52.30   $52.30  
  7 purchase totals = $1,127.00       $1,233.9234   $1,233.92   $1,233.90   $1,233.80