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 $184.80   5.314%   $194.6203   $194.62   $194.60   $194.60  
  Purchase #2 $63.81   7.593%   $68.6551   $68.66   $68.65   $68.70  
  Purchase #3 $84.88   3.104%   $87.5147   $87.51   $87.50   $87.50  
  Purchase #4 $206.86   7.251%   $221.8594   $221.86   $221.85   $221.90  
  Purchase #5 $123.55   13.539%   $140.2774   $140.28   $140.30   $140.30  
  Purchase #6 $197.25   3.853%   $204.85   $204.85   $204.85   $204.90  
  Purchase #7 $104.40   4.400%   $108.9936   $108.99   $109.00   $109.00  
  7 purchase totals = $965.55       $1,026.7705   $1,026.77   $1,026.75   $1,026.90