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 $64.62   7.694%   $69.5919   $69.59   $69.60   $69.60  
  Purchase #2 $219.91   7.520%   $236.4472   $236.45   $236.45   $236.40  
  Purchase #3 $162.68   6.586%   $173.3941   $173.39   $173.40   $173.40  
  Purchase #4 $79.30   7.608%   $85.3331   $85.33   $85.35   $85.30  
  Purchase #5 $21.29   3.732%   $22.0845   $22.08   $22.10   $22.10  
  Purchase #6 $191.40   6.861%   $204.532   $204.53   $204.55   $204.50  
  Purchase #7 $197.98   3.823%   $205.5488   $205.55   $205.55   $205.50  
  7 purchase totals = $937.18       $996.9316   $996.92   $997.00   $996.80