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 $186.34   8.494%   $202.1677   $202.17   $202.15   $202.20  
  Purchase #2 $91.30   9.219%   $99.7169   $99.72   $99.70   $99.70  
  Purchase #3 $96.72   11.517%   $107.8592   $107.86   $107.85   $107.90  
  Purchase #4 $18.84   12.620%   $21.2176   $21.22   $21.20   $21.20  
  Purchase #5 $122.66   7.159%   $131.4412   $131.44   $131.45   $131.40  
  Purchase #6 $244.90   6.861%   $261.7026   $261.70   $261.70   $261.70  
  Purchase #7 $183.57   10.377%   $202.6191   $202.62   $202.60   $202.60  
  7 purchase totals = $944.33       $1,026.7243   $1,026.73   $1,026.65   $1,026.70