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 $231.33   7.434%   $248.5271   $248.53   $248.55   $248.50  
  Purchase #2 $30.89   13.235%   $34.9783   $34.98   $35.00   $35.00  
  Purchase #3 $160.70   9.441%   $175.8717   $175.87   $175.85   $175.90  
  Purchase #4 $216.28   3.172%   $223.1404   $223.14   $223.15   $223.10  
  Purchase #5 $67.92   10.659%   $75.1596   $75.16   $75.15   $75.20  
  Purchase #6 $233.88   10.634%   $258.7508   $258.75   $258.75   $258.80  
  Purchase #7 $55.52   8.370%   $60.167   $60.17   $60.15   $60.20  
  7 purchase totals = $996.52       $1,076.5949   $1,076.60   $1,076.60   $1,076.70