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 $237.61   3.418%   $245.7315   $245.73   $245.75   $245.70  
  Purchase #2 $79.51   9.315%   $86.9164   $86.92   $86.90   $86.90  
  Purchase #3 $205.59   8.471%   $223.0055   $223.01   $223.00   $223.00  
  Purchase #4 $23.51   13.749%   $26.7424   $26.74   $26.75   $26.70  
  Purchase #5 $91.44   6.798%   $97.6561   $97.66   $97.65   $97.70  
  Purchase #6 $166.80   4.451%   $174.2243   $174.22   $174.20   $174.20  
  Purchase #7 $150.44   7.694%   $162.0149   $162.01   $162.00   $162.00  
  7 purchase totals = $954.90       $1,016.2911   $1,016.29   $1,016.25   $1,016.20