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 $118.64   3.136%   $122.3606   $122.36   $122.35   $122.40  
  Purchase #2 $239.61   11.718%   $267.6875   $267.69   $267.70   $267.70  
  Purchase #3 $155.93   11.819%   $174.3594   $174.36   $174.35   $174.40  
  Purchase #4 $172.93   13.800%   $196.7943   $196.79   $196.80   $196.80  
  Purchase #5 $231.65   6.578%   $246.8879   $246.89   $246.90   $246.90  
  Purchase #6 $37.93   8.800%   $41.2678   $41.27   $41.25   $41.30  
  Purchase #7 $234.99   13.554%   $266.8405   $266.84   $266.85   $266.80  
  7 purchase totals = $1,191.68       $1,316.1980   $1,316.20   $1,316.20   $1,316.30