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 $52.25   12.695%   $58.8831   $58.88   $58.90   $58.90  
  Purchase #2 $243.30   4.122%   $253.3288   $253.33   $253.35   $253.30  
  Purchase #3 $222.78   7.855%   $240.2794   $240.28   $240.30   $240.30  
  Purchase #4 $140.50   9.811%   $154.2845   $154.28   $154.30   $154.30  
  Purchase #5 $234.30   8.378%   $253.9297   $253.93   $253.95   $253.90  
  Purchase #6 $247.96   3.546%   $256.7527   $256.75   $256.75   $256.80  
  Purchase #7 $162.62   10.241%   $179.2739   $179.27   $179.25   $179.30  
  7 purchase totals = $1,303.71       $1,396.7321   $1,396.72   $1,396.80   $1,396.80