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 $175.86   4.644%   $184.0269   $184.03   $184.05   $184.00  
  Purchase #2 $30.31   8.315%   $32.8303   $32.83   $32.85   $32.80  
  Purchase #3 $190.38   5.202%   $200.2836   $200.28   $200.30   $200.30  
  Purchase #4 $193.48   7.269%   $207.5441   $207.54   $207.55   $207.50  
  Purchase #5 $159.88   8.334%   $173.2044   $173.20   $173.20   $173.20  
  Purchase #6 $244.82   4.426%   $255.6557   $255.66   $255.65   $255.70  
  Purchase #7 $101.27   6.679%   $108.0338   $108.03   $108.05   $108.00  
  7 purchase totals = $1,096.00       $1,161.5788   $1,161.57   $1,161.65   $1,161.50