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 $59.34   6.771%   $63.3579   $63.36   $63.35   $63.40  
  Purchase #2 $39.78   11.806%   $44.4764   $44.48   $44.50   $44.50  
  Purchase #3 $185.31   5.785%   $196.0302   $196.03   $196.05   $196.00  
  Purchase #4 $226.57   13.855%   $257.9613   $257.96   $257.95   $258.00  
  Purchase #5 $180.88   10.196%   $199.3225   $199.32   $199.30   $199.30  
  Purchase #6 $247.91   11.854%   $277.2973   $277.30   $277.30   $277.30  
  Purchase #7 $101.99   6.249%   $108.3634   $108.36   $108.35   $108.40  
  7 purchase totals = $1,041.78       $1,146.8090   $1,146.81   $1,146.80   $1,146.90