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 $192.47   3.120%   $198.4751   $198.48   $198.50   $198.50  
  Purchase #2 $66.55   13.325%   $75.4178   $75.42   $75.40   $75.40  
  Purchase #3 $58.88   10.584%   $65.1119   $65.11   $65.10   $65.10  
  Purchase #4 $73.83   7.313%   $79.2292   $79.23   $79.25   $79.20  
  Purchase #5 $208.25   11.651%   $232.5132   $232.51   $232.50   $232.50  
  Purchase #6 $192.77   4.372%   $201.1979   $201.20   $201.20   $201.20  
  Purchase #7 $202.34   7.231%   $216.9712   $216.97   $216.95   $217.00  
  7 purchase totals = $995.09       $1,068.9163   $1,068.92   $1,068.90   $1,068.90