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 $144.91   13.683%   $164.738   $164.74   $164.75   $164.70  
  Purchase #2 $159.27   5.184%   $167.5266   $167.53   $167.55   $167.50  
  Purchase #3 $150.63   13.498%   $170.962   $170.96   $170.95   $171.00  
  Purchase #4 $207.92   5.565%   $219.4907   $219.49   $219.50   $219.50  
  Purchase #5 $220.39   10.659%   $243.8814   $243.88   $243.90   $243.90  
  Purchase #6 $247.59   4.481%   $258.6845   $258.68   $258.70   $258.70  
  Purchase #7 $48.36   3.304%   $49.9578   $49.96   $49.95   $50.00  
  7 purchase totals = $1,179.07       $1,275.2410   $1,275.24   $1,275.30   $1,275.30