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 $167.53   12.712%   $188.8264   $188.83   $188.85   $188.80  
  Purchase #2 $161.42   13.355%   $182.9776   $182.98   $183.00   $183.00  
  Purchase #3 $151.91   9.840%   $166.8579   $166.86   $166.85   $166.90  
  Purchase #4 $238.46   8.762%   $259.3539   $259.35   $259.35   $259.40  
  Purchase #5 $82.29   8.675%   $89.4287   $89.43   $89.45   $89.40  
  Purchase #6 $85.84   5.267%   $90.3612   $90.36   $90.35   $90.40  
  Purchase #7 $203.28   11.114%   $225.8725   $225.87   $225.85   $225.90  
  7 purchase totals = $1,090.73       $1,203.6782   $1,203.68   $1,203.70   $1,203.80