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 $47.77   11.208%   $53.1241   $53.12   $53.10   $53.10  
  Purchase #2 $55.27   9.709%   $60.6362   $60.64   $60.65   $60.60  
  Purchase #3 $13.78   5.104%   $14.4833   $14.48   $14.50   $14.50  
  Purchase #4 $95.79   3.456%   $99.1005   $99.10   $99.10   $99.10  
  Purchase #5 $92.44   5.691%   $97.7008   $97.70   $97.70   $97.70  
  Purchase #6 $224.79   3.259%   $232.1159   $232.12   $232.10   $232.10  
  Purchase #7 $33.73   12.681%   $38.0073   $38.01   $38.00   $38.00  
  7 purchase totals = $563.57       $595.1681   $595.17   $595.15   $595.10