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 $193.95   3.386%   $200.5171   $200.52   $200.50   $200.50  
  Purchase #2 $179.74   9.846%   $197.4372   $197.44   $197.45   $197.40  
  Purchase #3 $244.32   12.296%   $274.3616   $274.36   $274.35   $274.40  
  Purchase #4 $59.84   11.817%   $66.9113   $66.91   $66.90   $66.90  
  Purchase #5 $9.53   7.815%   $10.2748   $10.27   $10.25   $10.30  
  Purchase #6 $222.31   7.533%   $239.0566   $239.06   $239.05   $239.10  
  Purchase #7 $198.35   10.786%   $219.744   $219.74   $219.75   $219.70  
  7 purchase totals = $1,108.04       $1,208.3026   $1,208.30   $1,208.25   $1,208.30