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 $108.83   12.277%   $122.1911   $122.19   $122.20   $122.20  
  Purchase #2 $226.57   6.635%   $241.6029   $241.60   $241.60   $241.60  
  Purchase #3 $166.74   11.849%   $186.497   $186.50   $186.50   $186.50  
  Purchase #4 $154.70   5.816%   $163.6974   $163.70   $163.70   $163.70  
  Purchase #5 $223.42   9.336%   $244.2785   $244.28   $244.30   $244.30  
  Purchase #6 $152.68   6.192%   $162.1339   $162.13   $162.15   $162.10  
  Purchase #7 $25.85   13.444%   $29.3253   $29.33   $29.35   $29.30  
  7 purchase totals = $1,058.79       $1,149.7261   $1,149.73   $1,149.80   $1,149.70