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 $182.44   12.204%   $204.705   $204.71   $204.70   $204.70  
  Purchase #2 $133.67   12.698%   $150.6434   $150.64   $150.65   $150.60  
  Purchase #3 $67.27   6.621%   $71.7239   $71.72   $71.70   $71.70  
  Purchase #4 $54.45   5.636%   $57.5188   $57.52   $57.50   $57.50  
  Purchase #5 $234.76   6.544%   $250.1227   $250.12   $250.10   $250.10  
  Purchase #6 $224.53   10.285%   $247.6229   $247.62   $247.60   $247.60  
  Purchase #7 $109.53   9.560%   $120.0011   $120.00   $120.00   $120.00  
  7 purchase totals = $1,006.65       $1,102.3378   $1,102.33   $1,102.25   $1,102.20