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 $214.52   13.570%   $243.6304   $243.63   $243.65   $243.60  
  Purchase #2 $7.40   6.394%   $7.8732   $7.87   $7.85   $7.90  
  Purchase #3 $240.65   6.284%   $255.7724   $255.77   $255.75   $255.80  
  Purchase #4 $96.85   12.459%   $108.9165   $108.92   $108.90   $108.90  
  Purchase #5 $196.35   3.122%   $202.48   $202.48   $202.50   $202.50  
  Purchase #6 $248.92   13.583%   $282.7308   $282.73   $282.75   $282.70  
  Purchase #7 $108.47   11.817%   $121.2879   $121.29   $121.30   $121.30  
  7 purchase totals = $1,113.16       $1,222.6912   $1,222.69   $1,222.70   $1,222.70