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 $197.96   8.602%   $214.9885   $214.99   $215.00   $215.00  
  Purchase #2 $5.70   8.814%   $6.2024   $6.20   $6.20   $6.20  
  Purchase #3 $139.99   5.384%   $147.5271   $147.53   $147.55   $147.50  
  Purchase #4 $35.33   3.306%   $36.498   $36.50   $36.50   $36.50  
  Purchase #5 $233.40   4.625%   $244.1948   $244.19   $244.20   $244.20  
  Purchase #6 $68.50   8.743%   $74.489   $74.49   $74.50   $74.50  
  Purchase #7 $111.32   6.503%   $118.5591   $118.56   $118.55   $118.60  
  7 purchase totals = $792.20       $842.4589   $842.46   $842.50   $842.50