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 $225.36   12.644%   $253.8545   $253.85   $253.85   $253.90  
  Purchase #2 $131.47   3.672%   $136.2976   $136.30   $136.30   $136.30  
  Purchase #3 $161.63   5.346%   $170.2707   $170.27   $170.25   $170.30  
  Purchase #4 $108.81   7.152%   $116.5921   $116.59   $116.60   $116.60  
  Purchase #5 $52.91   4.268%   $55.1682   $55.17   $55.15   $55.20  
  Purchase #6 $220.55   13.182%   $249.6229   $249.62   $249.60   $249.60  
  Purchase #7 $191.56   6.871%   $204.7221   $204.72   $204.70   $204.70  
  7 purchase totals = $1,092.29       $1,186.5281   $1,186.52   $1,186.45   $1,186.60