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 $59.39   7.134%   $63.6269   $63.63   $63.65   $63.60  
  Purchase #2 $90.74   9.607%   $99.4574   $99.46   $99.45   $99.50  
  Purchase #3 $50.39   9.293%   $55.0727   $55.07   $55.05   $55.10  
  Purchase #4 $129.83   9.693%   $142.4144   $142.41   $142.40   $142.40  
  Purchase #5 $213.45   7.281%   $228.9913   $228.99   $229.00   $229.00  
  Purchase #6 $246.98   6.270%   $262.4656   $262.47   $262.45   $262.50  
  Purchase #7 $195.89   6.282%   $208.1958   $208.20   $208.20   $208.20  
  7 purchase totals = $986.67       $1,060.2241   $1,060.23   $1,060.20   $1,060.30