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 $46.97   10.186%   $51.7544   $51.75   $51.75   $51.80  
  Purchase #2 $247.42   10.218%   $272.7014   $272.70   $272.70   $272.70  
  Purchase #3 $200.47   5.653%   $211.8026   $211.80   $211.80   $211.80  
  Purchase #4 $246.49   4.548%   $257.7004   $257.70   $257.70   $257.70  
  Purchase #5 $88.31   7.306%   $94.7619   $94.76   $94.75   $94.80  
  Purchase #6 $230.36   8.775%   $250.5741   $250.57   $250.55   $250.60  
  Purchase #7 $55.61   13.208%   $62.955   $62.96   $62.95   $63.00  
  7 purchase totals = $1,115.63       $1,202.2498   $1,202.24   $1,202.20   $1,202.40