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 $210.47   11.576%   $234.834   $234.83   $234.85   $234.80  
  Purchase #2 $132.26   12.557%   $148.8679   $148.87   $148.85   $148.90  
  Purchase #3 $184.36   3.591%   $190.9804   $190.98   $191.00   $191.00  
  Purchase #4 $118.88   4.601%   $124.3497   $124.35   $124.35   $124.30  
  Purchase #5 $140.46   7.157%   $150.5127   $150.51   $150.50   $150.50  
  Purchase #6 $231.41   6.536%   $246.535   $246.54   $246.55   $246.50  
  Purchase #7 $16.39   8.741%   $17.8226   $17.82   $17.80   $17.80  
  7 purchase totals = $1,034.23       $1,113.9023   $1,113.90   $1,113.90   $1,113.80