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 $173.51   7.437%   $186.4139   $186.41   $186.40   $186.40  
  Purchase #2 $96.59   8.137%   $104.4495   $104.45   $104.45   $104.40  
  Purchase #3 $115.57   12.258%   $129.7366   $129.74   $129.75   $129.70  
  Purchase #4 $221.49   4.836%   $232.2013   $232.20   $232.20   $232.20  
  Purchase #5 $17.50   12.577%   $19.701   $19.70   $19.70   $19.70  
  Purchase #6 $89.66   11.540%   $100.0068   $100.01   $100.00   $100.00  
  Purchase #7 $236.86   4.628%   $247.8219   $247.82   $247.80   $247.80  
  7 purchase totals = $951.18       $1,020.3310   $1,020.33   $1,020.30   $1,020.20