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 $82.83   13.322%   $93.8646   $93.86   $93.85   $93.90  
  Purchase #2 $186.91   3.488%   $193.4294   $193.43   $193.45   $193.40  
  Purchase #3 $227.33   4.839%   $238.3305   $238.33   $238.35   $238.30  
  Purchase #4 $56.74   4.690%   $59.4011   $59.40   $59.40   $59.40  
  Purchase #5 $138.80   9.360%   $151.7917   $151.79   $151.80   $151.80  
  Purchase #6 $168.95   9.676%   $185.2976   $185.30   $185.30   $185.30  
  Purchase #7 $232.26   7.524%   $249.7352   $249.74   $249.75   $249.70  
  7 purchase totals = $1,093.82       $1,171.8501   $1,171.85   $1,171.90   $1,171.80