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 $24.29   11.744%   $27.1426   $27.14   $27.15   $27.10  
  Purchase #2 $149.49   7.243%   $160.3176   $160.32   $160.30   $160.30  
  Purchase #3 $11.75   8.610%   $12.7617   $12.76   $12.75   $12.80  
  Purchase #4 $57.99   5.194%   $61.002   $61.00   $61.00   $61.00  
  Purchase #5 $159.91   13.376%   $181.2996   $181.30   $181.30   $181.30  
  Purchase #6 $139.94   12.327%   $157.1904   $157.19   $157.20   $157.20  
  Purchase #7 $152.67   5.340%   $160.8226   $160.82   $160.80   $160.80  
  7 purchase totals = $696.04       $760.5365   $760.53   $760.50   $760.50