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 $44.46   10.823%   $49.2719   $49.27   $49.25   $49.30  
  Purchase #2 $63.30   3.499%   $65.5149   $65.51   $65.50   $65.50  
  Purchase #3 $201.79   10.734%   $223.4501   $223.45   $223.45   $223.50  
  Purchase #4 $98.52   7.840%   $106.244   $106.24   $106.25   $106.20  
  Purchase #5 $250.74   12.713%   $282.6166   $282.62   $282.60   $282.60  
  Purchase #6 $109.81   13.192%   $124.2961   $124.30   $124.30   $124.30  
  Purchase #7 $41.70   6.258%   $44.3096   $44.31   $44.30   $44.30  
  7 purchase totals = $810.32       $895.7032   $895.70   $895.65   $895.70