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 $227.36   12.234%   $255.1752   $255.18   $255.20   $255.20  
  Purchase #2 $149.52   4.803%   $156.7014   $156.70   $156.70   $156.70  
  Purchase #3 $165.62   3.377%   $171.213   $171.21   $171.20   $171.20  
  Purchase #4 $238.26   10.382%   $262.9962   $263.00   $263.00   $263.00  
  Purchase #5 $214.93   9.438%   $235.2151   $235.22   $235.20   $235.20  
  Purchase #6 $226.77   3.240%   $234.1173   $234.12   $234.10   $234.10  
  Purchase #7 $155.50   5.154%   $163.5145   $163.51   $163.50   $163.50  
  7 purchase totals = $1,377.96       $1,478.9327   $1,478.94   $1,478.90   $1,478.90