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 $57.64   13.836%   $65.6151   $65.62   $65.60   $65.60  
  Purchase #2 $202.64   5.223%   $213.2239   $213.22   $213.20   $213.20  
  Purchase #3 $204.82   10.206%   $225.7239   $225.72   $225.70   $225.70  
  Purchase #4 $21.41   11.294%   $23.828   $23.83   $23.85   $23.80  
  Purchase #5 $49.73   11.543%   $55.4703   $55.47   $55.45   $55.50  
  Purchase #6 $145.31   5.117%   $152.7455   $152.75   $152.75   $152.70  
  Purchase #7 $110.94   10.483%   $122.5698   $122.57   $122.55   $122.60  
  7 purchase totals = $792.49       $859.1765   $859.18   $859.10   $859.10