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 $245.66   9.423%   $268.8085   $268.81   $268.80   $268.80  
  Purchase #2 $180.66   4.283%   $188.3977   $188.40   $188.40   $188.40  
  Purchase #3 $46.81   8.434%   $50.758   $50.76   $50.75   $50.80  
  Purchase #4 $197.57   11.310%   $219.9152   $219.92   $219.90   $219.90  
  Purchase #5 $231.53   12.714%   $260.9667   $260.97   $260.95   $261.00  
  Purchase #6 $23.57   8.294%   $25.5249   $25.52   $25.50   $25.50  
  Purchase #7 $22.84   7.795%   $24.6204   $24.62   $24.60   $24.60  
  7 purchase totals = $948.64       $1,038.9914   $1,039.00   $1,038.90   $1,039.00