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 $242.94   6.381%   $258.442   $258.44   $258.45   $258.40  
  Purchase #2 $59.48   5.240%   $62.5968   $62.60   $62.60   $62.60  
  Purchase #3 $212.52   6.745%   $226.8545   $226.85   $226.85   $226.90  
  Purchase #4 $207.87   10.483%   $229.661   $229.66   $229.65   $229.70  
  Purchase #5 $146.85   6.571%   $156.4995   $156.50   $156.50   $156.50  
  Purchase #6 $108.80   6.702%   $116.0918   $116.09   $116.10   $116.10  
  Purchase #7 $176.64   13.550%   $200.5747   $200.57   $200.55   $200.60  
  7 purchase totals = $1,155.10       $1,250.7203   $1,250.71   $1,250.70   $1,250.80