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 $176.49   4.801%   $184.9633   $184.96   $184.95   $185.00  
  Purchase #2 $238.34   12.440%   $267.9895   $267.99   $268.00   $268.00  
  Purchase #3 $20.43   3.121%   $21.0676   $21.07   $21.05   $21.10  
  Purchase #4 $184.75   9.873%   $202.9904   $202.99   $203.00   $203.00  
  Purchase #5 $26.90   6.607%   $28.6773   $28.68   $28.70   $28.70  
  Purchase #6 $233.63   11.472%   $260.432   $260.43   $260.45   $260.40  
  Purchase #7 $52.90   6.265%   $56.2142   $56.21   $56.20   $56.20  
  7 purchase totals = $933.44       $1,022.3343   $1,022.33   $1,022.35   $1,022.40