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 $184.25   7.347%   $197.7868   $197.79   $197.80   $197.80  
  Purchase #2 $43.52   7.146%   $46.6299   $46.63   $46.65   $46.60  
  Purchase #3 $109.87   11.761%   $122.7918   $122.79   $122.80   $122.80  
  Purchase #4 $187.88   10.353%   $207.3312   $207.33   $207.35   $207.30  
  Purchase #5 $178.90   12.294%   $200.894   $200.89   $200.90   $200.90  
  Purchase #6 $162.73   6.728%   $173.6785   $173.68   $173.70   $173.70  
  Purchase #7 $65.97   6.721%   $70.4038   $70.40   $70.40   $70.40  
  7 purchase totals = $933.12       $1,019.5160   $1,019.51   $1,019.60   $1,019.50