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 $91.42   3.211%   $94.3555   $94.36   $94.35   $94.40  
  Purchase #2 $246.61   12.630%   $277.7568   $277.76   $277.75   $277.80  
  Purchase #3 $55.90   11.371%   $62.2564   $62.26   $62.25   $62.30  
  Purchase #4 $157.90   11.741%   $176.439   $176.44   $176.45   $176.40  
  Purchase #5 $91.47   6.870%   $97.754   $97.75   $97.75   $97.80  
  Purchase #6 $198.49   12.773%   $223.8431   $223.84   $223.85   $223.80  
  Purchase #7 $57.93   12.597%   $65.2274   $65.23   $65.25   $65.20  
  7 purchase totals = $899.72       $997.6322   $997.64   $997.65   $997.70