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 $69.40   11.819%   $77.6024   $77.60   $77.60   $77.60  
  Purchase #2 $156.71   6.664%   $167.1532   $167.15   $167.15   $167.20  
  Purchase #3 $159.68   8.817%   $173.759   $173.76   $173.75   $173.80  
  Purchase #4 $130.53   13.300%   $147.8905   $147.89   $147.90   $147.90  
  Purchase #5 $167.77   9.783%   $184.1829   $184.18   $184.20   $184.20  
  Purchase #6 $190.98   3.484%   $197.6337   $197.63   $197.65   $197.60  
  Purchase #7 $232.93   7.366%   $250.0876   $250.09   $250.10   $250.10  
  7 purchase totals = $1,108.00       $1,198.3093   $1,198.30   $1,198.35   $1,198.40