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 $205.76   11.761%   $229.9594   $229.96   $229.95   $230.00  
  Purchase #2 $215.98   3.835%   $224.2628   $224.26   $224.25   $224.30  
  Purchase #3 $98.69   12.462%   $110.9887   $110.99   $111.00   $111.00  
  Purchase #4 $171.49   7.832%   $184.9211   $184.92   $184.90   $184.90  
  Purchase #5 $23.26   9.412%   $25.4492   $25.45   $25.45   $25.40  
  Purchase #6 $179.33   5.253%   $188.7502   $188.75   $188.75   $188.80  
  Purchase #7 $175.37   9.180%   $191.469   $191.47   $191.45   $191.50  
  7 purchase totals = $1,069.88       $1,155.8004   $1,155.80   $1,155.75   $1,155.90