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 $5.42   5.844%   $5.7367   $5.74   $5.75   $5.70  
  Purchase #2 $170.71   13.263%   $193.3513   $193.35   $193.35   $193.40  
  Purchase #3 $147.32   13.265%   $166.862   $166.86   $166.85   $166.90  
  Purchase #4 $96.72   7.731%   $104.1974   $104.20   $104.20   $104.20  
  Purchase #5 $20.66   7.595%   $22.2291   $22.23   $22.25   $22.20  
  Purchase #6 $195.57   9.798%   $214.7319   $214.73   $214.75   $214.70  
  Purchase #7 $223.68   9.708%   $245.3949   $245.39   $245.40   $245.40  
  7 purchase totals = $860.08       $952.5033   $952.50   $952.55   $952.50