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 $205.95   9.822%   $226.1784   $226.18   $226.20   $226.20  
  Purchase #2 $189.86   4.585%   $198.5651   $198.57   $198.55   $198.60  
  Purchase #3 $112.58   4.837%   $118.0255   $118.03   $118.05   $118.00  
  Purchase #4 $92.63   11.287%   $103.0851   $103.09   $103.10   $103.10  
  Purchase #5 $237.34   9.776%   $260.5424   $260.54   $260.55   $260.50  
  Purchase #6 $98.49   11.794%   $110.1059   $110.11   $110.10   $110.10  
  Purchase #7 $174.56   11.326%   $194.3307   $194.33   $194.35   $194.30  
  7 purchase totals = $1,111.41       $1,210.8331   $1,210.85   $1,210.90   $1,210.80