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 $152.66   6.242%   $162.189   $162.19   $162.20   $162.20  
  Purchase #2 $201.30   3.319%   $207.9811   $207.98   $208.00   $208.00  
  Purchase #3 $6.79   3.362%   $7.0183   $7.02   $7.00   $7.00  
  Purchase #4 $58.26   9.474%   $63.7796   $63.78   $63.80   $63.80  
  Purchase #5 $196.44   9.129%   $214.373   $214.37   $214.35   $214.40  
  Purchase #6 $44.53   5.291%   $46.8861   $46.89   $46.90   $46.90  
  Purchase #7 $7.37   6.787%   $7.8702   $7.87   $7.85   $7.90  
  7 purchase totals = $667.35       $710.0973   $710.10   $710.10   $710.20