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 $53.47   11.744%   $59.7495   $59.75   $59.75   $59.70  
  Purchase #2 $92.57   5.625%   $97.7771   $97.78   $97.80   $97.80  
  Purchase #3 $38.68   13.274%   $43.8144   $43.81   $43.80   $43.80  
  Purchase #4 $176.48   9.787%   $193.7521   $193.75   $193.75   $193.80  
  Purchase #5 $248.39   11.683%   $277.4094   $277.41   $277.40   $277.40  
  Purchase #6 $167.94   10.767%   $186.0221   $186.02   $186.00   $186.00  
  Purchase #7 $38.28   7.486%   $41.1456   $41.15   $41.15   $41.10  
  7 purchase totals = $815.81       $899.6702   $899.67   $899.65   $899.60