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 $142.28   5.416%   $149.9859   $149.99   $150.00   $150.00  
  Purchase #2 $103.79   5.810%   $109.8202   $109.82   $109.80   $109.80  
  Purchase #3 $158.39   9.521%   $173.4703   $173.47   $173.45   $173.50  
  Purchase #4 $233.93   10.471%   $258.4248   $258.42   $258.40   $258.40  
  Purchase #5 $238.57   4.526%   $249.3677   $249.37   $249.35   $249.40  
  Purchase #6 $74.72   3.316%   $77.1977   $77.20   $77.20   $77.20  
  Purchase #7 $100.43   10.647%   $111.1228   $111.12   $111.10   $111.10  
  7 purchase totals = $1,052.11       $1,129.3894   $1,129.39   $1,129.30   $1,129.40