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 $61.33   13.604%   $69.6733   $69.67   $69.65   $69.70  
  Purchase #2 $202.65   10.444%   $223.8148   $223.81   $223.80   $223.80  
  Purchase #3 $77.69   9.724%   $85.2446   $85.24   $85.25   $85.20  
  Purchase #4 $62.75   7.514%   $67.465   $67.47   $67.45   $67.50  
  Purchase #5 $58.90   8.309%   $63.794   $63.79   $63.80   $63.80  
  Purchase #6 $186.93   12.402%   $210.1131   $210.11   $210.10   $210.10  
  Purchase #7 $166.81   10.624%   $184.5319   $184.53   $184.55   $184.50  
  7 purchase totals = $817.06       $904.6367   $904.62   $904.60   $904.60