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 $227.25   8.386%   $246.3072   $246.31   $246.30   $246.30  
  Purchase #2 $112.68   11.549%   $125.6934   $125.69   $125.70   $125.70  
  Purchase #3 $135.66   12.343%   $152.4045   $152.40   $152.40   $152.40  
  Purchase #4 $116.67   3.279%   $120.4956   $120.50   $120.50   $120.50  
  Purchase #5 $156.76   11.607%   $174.9551   $174.96   $174.95   $175.00  
  Purchase #6 $209.73   6.699%   $223.7798   $223.78   $223.80   $223.80  
  Purchase #7 $67.99   11.411%   $75.7483   $75.75   $75.75   $75.70  
  7 purchase totals = $1,026.74       $1,119.3839   $1,119.39   $1,119.40   $1,119.40