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 $216.59   9.740%   $237.6859   $237.69   $237.70   $237.70  
  Purchase #2 $169.95   10.166%   $187.2271   $187.23   $187.25   $187.20  
  Purchase #3 $109.47   8.165%   $118.4082   $118.41   $118.40   $118.40  
  Purchase #4 $160.61   10.106%   $176.8412   $176.84   $176.85   $176.80  
  Purchase #5 $17.43   6.498%   $18.5626   $18.56   $18.55   $18.60  
  Purchase #6 $206.71   13.631%   $234.8866   $234.89   $234.90   $234.90  
  Purchase #7 $55.47   11.831%   $62.0327   $62.03   $62.05   $62.00  
  7 purchase totals = $936.23       $1,035.6443   $1,035.65   $1,035.70   $1,035.60