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 $224.51   9.599%   $246.0607   $246.06   $246.05   $246.10  
  Purchase #2 $187.29   8.447%   $203.1104   $203.11   $203.10   $203.10  
  Purchase #3 $13.53   5.870%   $14.3242   $14.32   $14.30   $14.30  
  Purchase #4 $23.33   10.314%   $25.7363   $25.74   $25.75   $25.70  
  Purchase #5 $187.49   6.280%   $199.2644   $199.26   $199.25   $199.30  
  Purchase #6 $242.79   6.724%   $259.1152   $259.12   $259.10   $259.10  
  Purchase #7 $50.70   5.644%   $53.5615   $53.56   $53.55   $53.60  
  7 purchase totals = $929.64       $1,001.1727   $1,001.17   $1,001.10   $1,001.20