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 $203.45   7.431%   $218.5684   $218.57   $218.55   $218.60  
  Purchase #2 $224.34   12.247%   $251.8149   $251.81   $251.80   $251.80  
  Purchase #3 $15.49   9.331%   $16.9354   $16.94   $16.95   $16.90  
  Purchase #4 $92.90   11.398%   $103.4887   $103.49   $103.50   $103.50  
  Purchase #5 $167.41   7.592%   $180.1198   $180.12   $180.10   $180.10  
  Purchase #6 $155.47   12.547%   $174.9768   $174.98   $175.00   $175.00  
  Purchase #7 $99.67   7.838%   $107.4821   $107.48   $107.50   $107.50  
  7 purchase totals = $958.73       $1,053.3861   $1,053.39   $1,053.40   $1,053.40