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 $126.64   11.809%   $141.5949   $141.59   $141.60   $141.60  
  Purchase #2 $231.98   3.817%   $240.8347   $240.83   $240.85   $240.80  
  Purchase #3 $136.94   12.241%   $153.7028   $153.70   $153.70   $153.70  
  Purchase #4 $222.28   9.208%   $242.7475   $242.75   $242.75   $242.70  
  Purchase #5 $15.35   10.496%   $16.9611   $16.96   $16.95   $17.00  
  Purchase #6 $178.59   7.436%   $191.87   $191.87   $191.85   $191.90  
  Purchase #7 $238.98   11.216%   $265.784   $265.78   $265.80   $265.80  
  7 purchase totals = $1,150.76       $1,253.4950   $1,253.48   $1,253.50   $1,253.50