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 $61.86   10.297%   $68.2297   $68.23   $68.25   $68.20  
  Purchase #2 $104.58   10.317%   $115.3695   $115.37   $115.35   $115.40  
  Purchase #3 $246.44   5.653%   $260.3713   $260.37   $260.35   $260.40  
  Purchase #4 $101.74   7.824%   $109.7001   $109.70   $109.70   $109.70  
  Purchase #5 $151.38   11.510%   $168.8038   $168.80   $168.80   $168.80  
  Purchase #6 $107.83   9.160%   $117.7072   $117.71   $117.70   $117.70  
  Purchase #7 $160.46   10.767%   $177.7367   $177.74   $177.75   $177.70  
  7 purchase totals = $934.29       $1,017.9183   $1,017.92   $1,017.90   $1,017.90