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 $229.45   10.706%   $254.0149   $254.01   $254.00   $254.00  
  Purchase #2 $237.87   5.410%   $250.7388   $250.74   $250.75   $250.70  
  Purchase #3 $183.60   11.149%   $204.0696   $204.07   $204.05   $204.10  
  Purchase #4 $239.27   10.157%   $263.5727   $263.57   $263.55   $263.60  
  Purchase #5 $58.32   4.620%   $61.0144   $61.01   $61.00   $61.00  
  Purchase #6 $28.90   10.407%   $31.9076   $31.91   $31.90   $31.90  
  Purchase #7 $183.79   6.664%   $196.0378   $196.04   $196.05   $196.00  
  7 purchase totals = $1,161.20       $1,261.3558   $1,261.35   $1,261.30   $1,261.30