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 $228.80   13.720%   $260.1914   $260.19   $260.20   $260.20  
  Purchase #2 $40.98   7.869%   $44.2047   $44.20   $44.20   $44.20  
  Purchase #3 $160.73   10.387%   $177.425   $177.43   $177.45   $177.40  
  Purchase #4 $72.48   6.544%   $77.2231   $77.22   $77.20   $77.20  
  Purchase #5 $173.64   10.231%   $191.4051   $191.41   $191.40   $191.40  
  Purchase #6 $152.54   12.805%   $172.0727   $172.07   $172.05   $172.10  
  Purchase #7 $231.30   6.663%   $246.7115   $246.71   $246.70   $246.70  
  7 purchase totals = $1,060.47       $1,169.2335   $1,169.23   $1,169.20   $1,169.20