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 $57.33   8.116%   $61.9829   $61.98   $62.00   $62.00  
  Purchase #2 $26.51   11.682%   $29.6069   $29.61   $29.60   $29.60  
  Purchase #3 $30.72   3.668%   $31.8468   $31.85   $31.85   $31.80  
  Purchase #4 $55.70   4.754%   $58.348   $58.35   $58.35   $58.30  
  Purchase #5 $108.91   10.136%   $119.9491   $119.95   $119.95   $119.90  
  Purchase #6 $202.75   4.167%   $211.1986   $211.20   $211.20   $211.20  
  Purchase #7 $42.41   4.678%   $44.3939   $44.39   $44.40   $44.40  
  7 purchase totals = $524.33       $557.3262   $557.33   $557.35   $557.20