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 $46.39   11.196%   $51.5838   $51.58   $51.60   $51.60  
  Purchase #2 $167.97   10.465%   $185.5481   $185.55   $185.55   $185.50  
  Purchase #3 $183.56   11.476%   $204.6253   $204.63   $204.65   $204.60  
  Purchase #4 $103.93   6.727%   $110.9214   $110.92   $110.90   $110.90  
  Purchase #5 $101.59   8.571%   $110.2973   $110.30   $110.30   $110.30  
  Purchase #6 $107.25   11.330%   $119.4014   $119.40   $119.40   $119.40  
  Purchase #7 $224.65   8.258%   $243.2016   $243.20   $243.20   $243.20  
  7 purchase totals = $935.34       $1,025.5789   $1,025.58   $1,025.60   $1,025.50