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 $244.32   9.185%   $266.7608   $266.76   $266.75   $266.80  
  Purchase #2 $154.38   10.333%   $170.3321   $170.33   $170.35   $170.30  
  Purchase #3 $214.36   13.734%   $243.8002   $243.80   $243.80   $243.80  
  Purchase #4 $230.70   7.579%   $248.1848   $248.18   $248.20   $248.20  
  Purchase #5 $113.83   7.740%   $122.6404   $122.64   $122.65   $122.60  
  Purchase #6 $185.43   10.538%   $204.9706   $204.97   $204.95   $205.00  
  Purchase #7 $33.97   9.870%   $37.3228   $37.32   $37.30   $37.30  
  7 purchase totals = $1,176.99       $1,294.0117   $1,294.00   $1,294.00   $1,294.00