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 $69.43   13.211%   $78.6024   $78.60   $78.60   $78.60  
  Purchase #2 $30.84   10.266%   $34.006   $34.01   $34.00   $34.00  
  Purchase #3 $24.93   5.194%   $26.2249   $26.22   $26.20   $26.20  
  Purchase #4 $63.29   9.612%   $69.3734   $69.37   $69.35   $69.40  
  Purchase #5 $224.29   8.736%   $243.884   $243.88   $243.90   $243.90  
  Purchase #6 $246.64   7.760%   $265.7793   $265.78   $265.80   $265.80  
  Purchase #7 $6.48   12.493%   $7.2895   $7.29   $7.30   $7.30  
  7 purchase totals = $665.90       $725.1595   $725.15   $725.15   $725.20