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 $10.47   10.695%   $11.5898   $11.59   $11.60   $11.60  
  Purchase #2 $191.68   5.766%   $202.7323   $202.73   $202.75   $202.70  
  Purchase #3 $81.56   12.298%   $91.5902   $91.59   $91.60   $91.60  
  Purchase #4 $244.48   6.211%   $259.6647   $259.66   $259.65   $259.70  
  Purchase #5 $145.46   6.446%   $154.8364   $154.84   $154.85   $154.80  
  Purchase #6 $228.73   12.581%   $257.5065   $257.51   $257.50   $257.50  
  Purchase #7 $16.48   4.538%   $17.2279   $17.23   $17.25   $17.20  
  7 purchase totals = $918.86       $995.1478   $995.15   $995.20   $995.10