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 $237.37   12.786%   $267.7201   $267.72   $267.70   $267.70  
  Purchase #2 $192.57   6.229%   $204.5652   $204.57   $204.55   $204.60  
  Purchase #3 $203.61   5.722%   $215.2606   $215.26   $215.25   $215.30  
  Purchase #4 $211.77   12.625%   $238.506   $238.51   $238.50   $238.50  
  Purchase #5 $218.90   12.600%   $246.4814   $246.48   $246.50   $246.50  
  Purchase #6 $21.38   13.701%   $24.3093   $24.31   $24.30   $24.30  
  Purchase #7 $108.53   7.617%   $116.7967   $116.80   $116.80   $116.80  
  7 purchase totals = $1,194.13       $1,313.6393   $1,313.65   $1,313.60   $1,313.70