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 $204.50   13.467%   $232.04   $232.04   $232.05   $232.00  
  Purchase #2 $131.90   8.870%   $143.5995   $143.60   $143.60   $143.60  
  Purchase #3 $250.69   5.363%   $264.1345   $264.13   $264.15   $264.10  
  Purchase #4 $23.93   6.823%   $25.5627   $25.56   $25.55   $25.60  
  Purchase #5 $224.79   3.493%   $232.6419   $232.64   $232.65   $232.60  
  Purchase #6 $246.96   13.291%   $279.7835   $279.78   $279.80   $279.80  
  Purchase #7 $226.45   10.656%   $250.5805   $250.58   $250.60   $250.60  
  7 purchase totals = $1,309.22       $1,428.3426   $1,428.33   $1,428.40   $1,428.30