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 $61.56   8.750%   $66.9465   $66.95   $66.95   $66.90  
  Purchase #2 $141.98   3.764%   $147.3241   $147.32   $147.30   $147.30  
  Purchase #3 $120.86   3.550%   $125.1505   $125.15   $125.15   $125.20  
  Purchase #4 $44.74   5.871%   $47.3667   $47.37   $47.35   $47.40  
  Purchase #5 $70.62   9.215%   $77.1276   $77.13   $77.15   $77.10  
  Purchase #6 $131.61   10.371%   $145.2593   $145.26   $145.25   $145.30  
  Purchase #7 $230.34   7.384%   $247.3483   $247.35   $247.35   $247.30  
  7 purchase totals = $801.71       $856.5230   $856.53   $856.50   $856.50