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 $53.98   9.245%   $58.9705   $58.97   $58.95   $59.00  
  Purchase #2 $52.28   10.218%   $57.622   $57.62   $57.60   $57.60  
  Purchase #3 $246.90   4.378%   $257.7093   $257.71   $257.70   $257.70  
  Purchase #4 $15.42   10.516%   $17.0416   $17.04   $17.05   $17.00  
  Purchase #5 $201.70   13.328%   $228.5826   $228.58   $228.60   $228.60  
  Purchase #6 $119.69   6.550%   $127.5297   $127.53   $127.55   $127.50  
  Purchase #7 $238.84   9.207%   $260.83   $260.83   $260.85   $260.80  
  7 purchase totals = $928.81       $1,008.2857   $1,008.28   $1,008.30   $1,008.20