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 $77.86   12.249%   $87.3971   $87.40   $87.40   $87.40  
  Purchase #2 $194.81   7.811%   $210.0266   $210.03   $210.05   $210.00  
  Purchase #3 $136.40   12.794%   $153.851   $153.85   $153.85   $153.90  
  Purchase #4 $245.52   5.861%   $259.9099   $259.91   $259.90   $259.90  
  Purchase #5 $211.62   6.200%   $224.7404   $224.74   $224.75   $224.70  
  Purchase #6 $55.83   13.466%   $63.3481   $63.35   $63.35   $63.30  
  Purchase #7 $162.30   7.548%   $174.5504   $174.55   $174.55   $174.60  
  7 purchase totals = $1,084.34       $1,173.8235   $1,173.83   $1,173.85   $1,173.80