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 $250.46   7.463%   $269.1518   $269.15   $269.15   $269.20  
  Purchase #2 $112.27   10.241%   $123.7676   $123.77   $123.75   $123.80  
  Purchase #3 $69.50   7.551%   $74.7479   $74.75   $74.75   $74.70  
  Purchase #4 $72.66   6.467%   $77.3589   $77.36   $77.35   $77.40  
  Purchase #5 $52.82   13.334%   $59.863   $59.86   $59.85   $59.90  
  Purchase #6 $27.75   4.533%   $29.0079   $29.01   $29.00   $29.00  
  Purchase #7 $60.45   12.531%   $68.025   $68.03   $68.05   $68.00  
  7 purchase totals = $645.91       $701.9221   $701.93   $701.90   $702.00