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 $212.25   5.112%   $223.1002   $223.10   $223.10   $223.10  
  Purchase #2 $185.81   4.210%   $193.6326   $193.63   $193.65   $193.60  
  Purchase #3 $218.88   6.765%   $233.6872   $233.69   $233.70   $233.70  
  Purchase #4 $216.92   4.437%   $226.5447   $226.54   $226.55   $226.50  
  Purchase #5 $157.47   3.414%   $162.846   $162.85   $162.85   $162.80  
  Purchase #6 $233.90   13.374%   $265.1818   $265.18   $265.20   $265.20  
  Purchase #7 $21.57   11.838%   $24.1235   $24.12   $24.10   $24.10  
  7 purchase totals = $1,246.80       $1,329.1160   $1,329.11   $1,329.15   $1,329.00