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 $217.29   6.144%   $230.6403   $230.64   $230.65   $230.60  
  Purchase #2 $150.31   12.377%   $168.9139   $168.91   $168.90   $168.90  
  Purchase #3 $12.25   4.112%   $12.7537   $12.75   $12.75   $12.80  
  Purchase #4 $32.95   3.431%   $34.0805   $34.08   $34.10   $34.10  
  Purchase #5 $114.84   5.161%   $120.7669   $120.77   $120.75   $120.80  
  Purchase #6 $200.70   4.282%   $209.294   $209.29   $209.30   $209.30  
  Purchase #7 $205.47   5.223%   $216.2017   $216.20   $216.20   $216.20  
  7 purchase totals = $933.81       $992.6510   $992.64   $992.65   $992.70