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 $98.58   11.294%   $109.7136   $109.71   $109.70   $109.70  
  Purchase #2 $198.37   9.374%   $216.9652   $216.97   $216.95   $217.00  
  Purchase #3 $200.34   3.246%   $206.843   $206.84   $206.85   $206.80  
  Purchase #4 $231.70   8.476%   $251.3389   $251.34   $251.35   $251.30  
  Purchase #5 $139.69   5.721%   $147.6817   $147.68   $147.70   $147.70  
  Purchase #6 $176.33   10.644%   $195.0986   $195.10   $195.10   $195.10  
  Purchase #7 $187.59   13.334%   $212.6033   $212.60   $212.60   $212.60  
  7 purchase totals = $1,232.60       $1,340.2443   $1,340.24   $1,340.25   $1,340.20