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 $245.88   12.111%   $275.6585   $275.66   $275.65   $275.70  
  Purchase #2 $238.99   5.580%   $252.3256   $252.33   $252.35   $252.30  
  Purchase #3 $30.78   9.142%   $33.5939   $33.59   $33.60   $33.60  
  Purchase #4 $249.60   13.792%   $284.0248   $284.02   $284.00   $284.00  
  Purchase #5 $222.77   10.771%   $246.7646   $246.76   $246.75   $246.80  
  Purchase #6 $157.97   6.253%   $167.8479   $167.85   $167.85   $167.80  
  Purchase #7 $129.94   9.662%   $142.4948   $142.49   $142.50   $142.50  
  7 purchase totals = $1,275.93       $1,402.7101   $1,402.70   $1,402.70   $1,402.70