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 $187.53   6.671%   $200.0401   $200.04   $200.05   $200.00  
  Purchase #2 $68.75   5.197%   $72.3229   $72.32   $72.30   $72.30  
  Purchase #3 $142.32   4.123%   $148.1879   $148.19   $148.20   $148.20  
  Purchase #4 $156.53   12.395%   $175.9319   $175.93   $175.95   $175.90  
  Purchase #5 $86.88   7.841%   $93.6923   $93.69   $93.70   $93.70  
  Purchase #6 $223.33   3.126%   $230.3113   $230.31   $230.30   $230.30  
  Purchase #7 $5.57   12.377%   $6.2594   $6.26   $6.25   $6.30  
  7 purchase totals = $870.91       $926.7458   $926.74   $926.75   $926.70