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 $54.33   6.711%   $57.9761   $57.98   $58.00   $58.00  
  Purchase #2 $202.36   13.391%   $229.458   $229.46   $229.45   $229.50  
  Purchase #3 $116.89   9.352%   $127.8216   $127.82   $127.80   $127.80  
  Purchase #4 $179.58   11.683%   $200.5603   $200.56   $200.55   $200.60  
  Purchase #5 $177.27   9.325%   $193.8004   $193.80   $193.80   $193.80  
  Purchase #6 $157.87   11.613%   $176.2034   $176.20   $176.20   $176.20  
  Purchase #7 $239.30   9.484%   $261.9952   $262.00   $262.00   $262.00  
  7 purchase totals = $1,127.60       $1,247.8150   $1,247.82   $1,247.80   $1,247.90