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 $146.94   3.264%   $151.7361   $151.74   $151.75   $151.70  
  Purchase #2 $196.82   13.728%   $223.8394   $223.84   $223.85   $223.80  
  Purchase #3 $105.47   9.214%   $115.188   $115.19   $115.20   $115.20  
  Purchase #4 $209.59   4.154%   $218.2964   $218.30   $218.30   $218.30  
  Purchase #5 $108.68   13.148%   $122.9692   $122.97   $122.95   $123.00  
  Purchase #6 $34.76   3.294%   $35.905   $35.91   $35.90   $35.90  
  Purchase #7 $141.67   11.737%   $158.2978   $158.30   $158.30   $158.30  
  7 purchase totals = $943.93       $1,026.2319   $1,026.25   $1,026.25   $1,026.20