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 $56.36   11.257%   $62.7044   $62.70   $62.70   $62.70  
  Purchase #2 $142.78   6.326%   $151.8123   $151.81   $151.80   $151.80  
  Purchase #3 $134.36   3.604%   $139.2023   $139.20   $139.20   $139.20  
  Purchase #4 $114.74   4.352%   $119.7335   $119.73   $119.75   $119.70  
  Purchase #5 $61.33   4.709%   $64.218   $64.22   $64.20   $64.20  
  Purchase #6 $249.32   13.239%   $282.3275   $282.33   $282.35   $282.30  
  Purchase #7 $191.26   5.210%   $201.2246   $201.22   $201.20   $201.20  
  7 purchase totals = $950.15       $1,021.2226   $1,021.21   $1,021.20   $1,021.10