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 $111.96   5.393%   $117.998   $118.00   $118.00   $118.00  
  Purchase #2 $223.35   13.558%   $253.6318   $253.63   $253.65   $253.60  
  Purchase #3 $59.30   4.136%   $61.7526   $61.75   $61.75   $61.80  
  Purchase #4 $89.91   7.212%   $96.3943   $96.39   $96.40   $96.40  
  Purchase #5 $211.25   7.326%   $226.7262   $226.73   $226.75   $226.70  
  Purchase #6 $75.77   5.430%   $79.8843   $79.88   $79.90   $79.90  
  Purchase #7 $40.31   11.852%   $45.0875   $45.09   $45.10   $45.10  
  7 purchase totals = $811.85       $881.4747   $881.47   $881.55   $881.50