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 $201.77   12.439%   $226.8682   $226.87   $226.85   $226.90  
  Purchase #2 $218.86   11.818%   $244.7249   $244.72   $244.70   $244.70  
  Purchase #3 $239.89   13.622%   $272.5678   $272.57   $272.55   $272.60  
  Purchase #4 $113.91   4.598%   $119.1476   $119.15   $119.15   $119.10  
  Purchase #5 $215.56   4.126%   $224.454   $224.45   $224.45   $224.50  
  Purchase #6 $60.28   11.273%   $67.0754   $67.08   $67.10   $67.10  
  Purchase #7 $10.44   8.160%   $11.2919   $11.29   $11.30   $11.30  
  7 purchase totals = $1,060.71       $1,166.1298   $1,166.13   $1,166.10   $1,166.20