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 $87.46   9.842%   $96.0678   $96.07   $96.05   $96.10  
  Purchase #2 $80.76   10.651%   $89.3617   $89.36   $89.35   $89.40  
  Purchase #3 $221.59   5.151%   $233.0041   $233.00   $233.00   $233.00  
  Purchase #4 $161.41   13.829%   $183.7314   $183.73   $183.75   $183.70  
  Purchase #5 $157.82   9.570%   $172.9234   $172.92   $172.90   $172.90  
  Purchase #6 $65.47   5.720%   $69.2149   $69.21   $69.20   $69.20  
  Purchase #7 $193.25   13.432%   $219.2073   $219.21   $219.20   $219.20  
  7 purchase totals = $967.76       $1,063.5106   $1,063.50   $1,063.45   $1,063.50