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 $126.26   6.579%   $134.5666   $134.57   $134.55   $134.60  
  Purchase #2 $112.36   9.244%   $122.7466   $122.75   $122.75   $122.70  
  Purchase #3 $219.29   8.428%   $237.7718   $237.77   $237.75   $237.80  
  Purchase #4 $59.93   5.427%   $63.1824   $63.18   $63.20   $63.20  
  Purchase #5 $125.97   4.106%   $131.1423   $131.14   $131.15   $131.10  
  Purchase #6 $98.74   12.201%   $110.7873   $110.79   $110.80   $110.80  
  Purchase #7 $73.74   5.691%   $77.9365   $77.94   $77.95   $77.90  
  7 purchase totals = $816.29       $878.1335   $878.14   $878.15   $878.10