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 $54.83   6.128%   $58.19   $58.19   $58.20   $58.20  
  Purchase #2 $134.40   3.141%   $138.6215   $138.62   $138.60   $138.60  
  Purchase #3 $7.40   12.597%   $8.3322   $8.33   $8.35   $8.30  
  Purchase #4 $228.57   3.459%   $236.4762   $236.48   $236.50   $236.50  
  Purchase #5 $87.44   9.812%   $96.0196   $96.02   $96.00   $96.00  
  Purchase #6 $55.62   11.256%   $61.8806   $61.88   $61.90   $61.90  
  Purchase #7 $153.49   8.553%   $166.618   $166.62   $166.60   $166.60  
  7 purchase totals = $721.75       $766.1381   $766.14   $766.15   $766.10