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 $174.32   7.169%   $186.817   $186.82   $186.80   $186.80  
  Purchase #2 $219.48   5.223%   $230.9434   $230.94   $230.95   $230.90  
  Purchase #3 $50.45   4.858%   $52.9009   $52.90   $52.90   $52.90  
  Purchase #4 $50.33   5.271%   $52.9829   $52.98   $53.00   $53.00  
  Purchase #5 $193.37   5.664%   $204.3225   $204.32   $204.30   $204.30  
  Purchase #6 $245.76   7.273%   $263.6341   $263.63   $263.65   $263.60  
  Purchase #7 $228.77   3.868%   $237.6188   $237.62   $237.60   $237.60  
  7 purchase totals = $1,162.48       $1,229.2196   $1,229.21   $1,229.20   $1,229.10