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 $204.53   5.182%   $215.1287   $215.13   $215.15   $215.10  
  Purchase #2 $90.99   6.821%   $97.1964   $97.20   $97.20   $97.20  
  Purchase #3 $144.56   8.415%   $156.7247   $156.72   $156.70   $156.70  
  Purchase #4 $26.34   12.202%   $29.554   $29.55   $29.55   $29.60  
  Purchase #5 $187.96   7.546%   $202.1435   $202.14   $202.15   $202.10  
  Purchase #6 $195.25   5.591%   $206.1664   $206.17   $206.15   $206.20  
  Purchase #7 $38.72   11.859%   $43.3118   $43.31   $43.30   $43.30  
  7 purchase totals = $888.35       $950.2255   $950.22   $950.20   $950.20