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 $153.77   13.674%   $174.7965   $174.80   $174.80   $174.80  
  Purchase #2 $72.97   8.751%   $79.3556   $79.36   $79.35   $79.40  
  Purchase #3 $112.75   10.250%   $124.3069   $124.31   $124.30   $124.30  
  Purchase #4 $226.27   6.812%   $241.6835   $241.68   $241.70   $241.70  
  Purchase #5 $244.75   13.359%   $277.4462   $277.45   $277.45   $277.40  
  Purchase #6 $85.45   4.562%   $89.3482   $89.35   $89.35   $89.30  
  Purchase #7 $236.86   7.398%   $254.3829   $254.38   $254.40   $254.40  
  7 purchase totals = $1,132.82       $1,241.3198   $1,241.33   $1,241.35   $1,241.30