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 $158.41   3.322%   $163.6724   $163.67   $163.65   $163.70  
  Purchase #2 $90.49   10.507%   $99.9978   $100.00   $100.00   $100.00  
  Purchase #3 $71.41   11.112%   $79.3451   $79.35   $79.35   $79.30  
  Purchase #4 $93.31   13.706%   $106.0991   $106.10   $106.10   $106.10  
  Purchase #5 $75.97   6.153%   $80.6444   $80.64   $80.65   $80.60  
  Purchase #6 $7.36   5.455%   $7.7615   $7.76   $7.75   $7.80  
  Purchase #7 $76.35   7.691%   $82.2221   $82.22   $82.20   $82.20  
  7 purchase totals = $573.30       $619.7424   $619.74   $619.70   $619.70