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 $55.92   6.536%   $59.5749   $59.57   $59.55   $59.60  
  Purchase #2 $115.58   9.386%   $126.4283   $126.43   $126.45   $126.40  
  Purchase #3 $214.70   9.617%   $235.3477   $235.35   $235.35   $235.30  
  Purchase #4 $148.67   10.350%   $164.0573   $164.06   $164.05   $164.10  
  Purchase #5 $213.79   4.530%   $223.4747   $223.47   $223.45   $223.50  
  Purchase #6 $214.78   10.453%   $237.231   $237.23   $237.25   $237.20  
  Purchase #7 $150.95   7.457%   $162.2063   $162.21   $162.20   $162.20  
  7 purchase totals = $1,114.39       $1,208.3202   $1,208.32   $1,208.30   $1,208.30