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 $92.74   6.241%   $98.5279   $98.53   $98.55   $98.50  
  Purchase #2 $184.36   4.295%   $192.2783   $192.28   $192.30   $192.30  
  Purchase #3 $162.71   6.408%   $173.1365   $173.14   $173.15   $173.10  
  Purchase #4 $246.49   10.838%   $273.2046   $273.20   $273.20   $273.20  
  Purchase #5 $77.84   12.218%   $87.3505   $87.35   $87.35   $87.40  
  Purchase #6 $107.70   8.374%   $116.7188   $116.72   $116.70   $116.70  
  Purchase #7 $74.97   7.798%   $80.8162   $80.82   $80.80   $80.80  
  7 purchase totals = $946.81       $1,022.0328   $1,022.04   $1,022.05   $1,022.00