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 $91.87   10.318%   $101.3491   $101.35   $101.35   $101.30  
  Purchase #2 $224.34   12.134%   $251.5614   $251.56   $251.55   $251.60  
  Purchase #3 $178.89   11.352%   $199.1976   $199.20   $199.20   $199.20  
  Purchase #4 $110.51   11.689%   $123.4275   $123.43   $123.45   $123.40  
  Purchase #5 $208.69   12.681%   $235.154   $235.15   $235.15   $235.20  
  Purchase #6 $190.42   5.865%   $201.5881   $201.59   $201.60   $201.60  
  Purchase #7 $68.51   8.539%   $74.3601   $74.36   $74.35   $74.40  
  7 purchase totals = $1,073.23       $1,186.6378   $1,186.64   $1,186.65   $1,186.70