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 $69.53   11.443%   $77.4863   $77.49   $77.50   $77.50  
  Purchase #2 $247.96   7.774%   $267.2364   $267.24   $267.25   $267.20  
  Purchase #3 $147.95   10.788%   $163.9108   $163.91   $163.90   $163.90  
  Purchase #4 $170.81   9.852%   $187.6382   $187.64   $187.65   $187.60  
  Purchase #5 $158.51   7.331%   $170.1304   $170.13   $170.15   $170.10  
  Purchase #6 $91.27   7.673%   $98.2731   $98.27   $98.25   $98.30  
  Purchase #7 $56.41   7.584%   $60.6881   $60.69   $60.70   $60.70  
  7 purchase totals = $942.44       $1,025.3633   $1,025.37   $1,025.40   $1,025.30