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 $73.84   4.787%   $77.3747   $77.37   $77.35   $77.40  
  Purchase #2 $224.82   12.612%   $253.1743   $253.17   $253.15   $253.20  
  Purchase #3 $131.45   13.600%   $149.3272   $149.33   $149.35   $149.30  
  Purchase #4 $154.86   13.853%   $176.3128   $176.31   $176.30   $176.30  
  Purchase #5 $233.55   5.286%   $245.8955   $245.90   $245.90   $245.90  
  Purchase #6 $106.37   11.492%   $118.594   $118.59   $118.60   $118.60  
  Purchase #7 $78.43   12.148%   $87.9577   $87.96   $87.95   $88.00  
  7 purchase totals = $1,003.32       $1,108.6362   $1,108.63   $1,108.60   $1,108.70