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 $106.36   11.430%   $118.5169   $118.52   $118.50   $118.50  
  Purchase #2 $248.83   10.787%   $275.6713   $275.67   $275.65   $275.70  
  Purchase #3 $158.36   13.596%   $179.8906   $179.89   $179.90   $179.90  
  Purchase #4 $65.67   8.640%   $71.3439   $71.34   $71.35   $71.30  
  Purchase #5 $241.39   9.809%   $265.0679   $265.07   $265.05   $265.10  
  Purchase #6 $70.93   7.187%   $76.0277   $76.03   $76.05   $76.00  
  Purchase #7 $229.37   11.752%   $256.3256   $256.33   $256.35   $256.30  
  7 purchase totals = $1,120.91       $1,242.8439   $1,242.85   $1,242.85   $1,242.80