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 $203.35   10.803%   $225.3179   $225.32   $225.30   $225.30  
  Purchase #2 $242.58   6.155%   $257.5108   $257.51   $257.50   $257.50  
  Purchase #3 $24.67   6.232%   $26.2074   $26.21   $26.20   $26.20  
  Purchase #4 $94.91   11.547%   $105.8693   $105.87   $105.85   $105.90  
  Purchase #5 $241.83   3.421%   $250.103   $250.10   $250.10   $250.10  
  Purchase #6 $96.36   12.437%   $108.3443   $108.34   $108.35   $108.30  
  Purchase #7 $77.98   6.155%   $82.7797   $82.78   $82.80   $82.80  
  7 purchase totals = $981.68       $1,056.1324   $1,056.13   $1,056.10   $1,056.10