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 $69.62   7.713%   $74.9898   $74.99   $75.00   $75.00  
  Purchase #2 $49.34   6.750%   $52.6705   $52.67   $52.65   $52.70  
  Purchase #3 $193.88   4.133%   $201.8931   $201.89   $201.90   $201.90  
  Purchase #4 $62.73   5.800%   $66.3683   $66.37   $66.35   $66.40  
  Purchase #5 $70.61   9.359%   $77.2184   $77.22   $77.20   $77.20  
  Purchase #6 $239.80   5.347%   $252.6221   $252.62   $252.60   $252.60  
  Purchase #7 $140.90   8.132%   $152.358   $152.36   $152.35   $152.40  
  7 purchase totals = $826.88       $878.1202   $878.12   $878.05   $878.20