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 $43.78   5.458%   $46.1695   $46.17   $46.15   $46.20  
  Purchase #2 $151.86   7.456%   $163.1827   $163.18   $163.20   $163.20  
  Purchase #3 $232.34   8.429%   $251.9239   $251.92   $251.90   $251.90  
  Purchase #4 $188.25   9.200%   $205.569   $205.57   $205.55   $205.60  
  Purchase #5 $65.48   12.463%   $73.6408   $73.64   $73.65   $73.60  
  Purchase #6 $119.56   5.695%   $126.3689   $126.37   $126.35   $126.40  
  Purchase #7 $140.74   9.767%   $154.4861   $154.49   $154.50   $154.50  
  7 purchase totals = $942.01       $1,021.3409   $1,021.34   $1,021.30   $1,021.40