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 $59.44   6.193%   $63.1211   $63.12   $63.10   $63.10  
  Purchase #2 $223.67   6.387%   $237.9558   $237.96   $237.95   $238.00  
  Purchase #3 $29.63   4.338%   $30.9153   $30.92   $30.90   $30.90  
  Purchase #4 $31.62   5.782%   $33.4483   $33.45   $33.45   $33.40  
  Purchase #5 $57.44   6.162%   $60.9795   $60.98   $61.00   $61.00  
  Purchase #6 $186.78   9.616%   $204.7408   $204.74   $204.75   $204.70  
  Purchase #7 $69.30   6.538%   $73.8308   $73.83   $73.85   $73.80  
  7 purchase totals = $657.88       $704.9916   $705.00   $705.00   $704.90