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 $62.86   5.227%   $66.1457   $66.15   $66.15   $66.10  
  Purchase #2 $209.27   6.738%   $223.3706   $223.37   $223.35   $223.40  
  Purchase #3 $200.46   3.332%   $207.1393   $207.14   $207.15   $207.10  
  Purchase #4 $143.71   3.117%   $148.1894   $148.19   $148.20   $148.20  
  Purchase #5 $216.73   5.365%   $228.3576   $228.36   $228.35   $228.40  
  Purchase #6 $58.39   5.379%   $61.5308   $61.53   $61.55   $61.50  
  Purchase #7 $225.79   5.804%   $238.8949   $238.89   $238.90   $238.90  
  7 purchase totals = $1,117.21       $1,173.6283   $1,173.63   $1,173.65   $1,173.60