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 $41.36   5.730%   $43.7299   $43.73   $43.75   $43.70  
  Purchase #2 $232.56   7.696%   $250.4578   $250.46   $250.45   $250.50  
  Purchase #3 $130.55   5.817%   $138.1441   $138.14   $138.15   $138.10  
  Purchase #4 $204.87   9.548%   $224.431   $224.43   $224.45   $224.40  
  Purchase #5 $226.84   6.591%   $241.791   $241.79   $241.80   $241.80  
  Purchase #6 $26.27   9.634%   $28.8009   $28.80   $28.80   $28.80  
  Purchase #7 $61.67   3.436%   $63.789   $63.79   $63.80   $63.80  
  7 purchase totals = $924.12       $991.1437   $991.14   $991.20   $991.10