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 $176.49   8.848%   $192.1058   $192.11   $192.10   $192.10  
  Purchase #2 $54.26   7.569%   $58.3669   $58.37   $58.35   $58.40  
  Purchase #3 $130.69   8.288%   $141.5216   $141.52   $141.50   $141.50  
  Purchase #4 $139.39   12.140%   $156.3119   $156.31   $156.30   $156.30  
  Purchase #5 $56.31   9.803%   $61.8301   $61.83   $61.85   $61.80  
  Purchase #6 $90.46   12.118%   $101.4219   $101.42   $101.40   $101.40  
  Purchase #7 $46.80   8.780%   $50.909   $50.91   $50.90   $50.90  
  7 purchase totals = $694.40       $762.4672   $762.47   $762.40   $762.40