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 $219.45   12.544%   $246.9778   $246.98   $247.00   $247.00  
  Purchase #2 $27.72   6.322%   $29.4725   $29.47   $29.45   $29.50  
  Purchase #3 $229.89   6.166%   $244.065   $244.07   $244.05   $244.10  
  Purchase #4 $209.29   12.210%   $234.8443   $234.84   $234.85   $234.80  
  Purchase #5 $246.80   6.677%   $263.2788   $263.28   $263.30   $263.30  
  Purchase #6 $113.33   13.214%   $128.3054   $128.31   $128.30   $128.30  
  Purchase #7 $210.97   5.123%   $221.778   $221.78   $221.80   $221.80  
  7 purchase totals = $1,257.45       $1,368.7218   $1,368.73   $1,368.75   $1,368.80