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 $202.68   9.558%   $222.0522   $222.05   $222.05   $222.10  
  Purchase #2 $101.33   11.863%   $113.3508   $113.35   $113.35   $113.40  
  Purchase #3 $168.50   5.201%   $177.2637   $177.26   $177.25   $177.30  
  Purchase #4 $67.29   11.339%   $74.92   $74.92   $74.90   $74.90  
  Purchase #5 $231.29   6.345%   $245.9654   $245.97   $245.95   $246.00  
  Purchase #6 $22.81   4.231%   $23.7751   $23.78   $23.80   $23.80  
  Purchase #7 $204.74   8.633%   $222.4152   $222.42   $222.40   $222.40  
  7 purchase totals = $998.64       $1,079.7424   $1,079.75   $1,079.70   $1,079.90