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 $126.49   7.554%   $136.0451   $136.05   $136.05   $136.00  
  Purchase #2 $245.94   12.241%   $276.0455   $276.05   $276.05   $276.00  
  Purchase #3 $143.99   13.818%   $163.8865   $163.89   $163.90   $163.90  
  Purchase #4 $66.97   9.547%   $73.3636   $73.36   $73.35   $73.40  
  Purchase #5 $163.30   7.726%   $175.9166   $175.92   $175.90   $175.90  
  Purchase #6 $66.93   7.844%   $72.18   $72.18   $72.20   $72.20  
  Purchase #7 $232.32   6.221%   $246.7726   $246.77   $246.75   $246.80  
  7 purchase totals = $1,045.94       $1,144.2099   $1,144.22   $1,144.20   $1,144.20