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 $132.90   10.620%   $147.014   $147.01   $147.00   $147.00  
  Purchase #2 $34.91   5.291%   $36.7571   $36.76   $36.75   $36.80  
  Purchase #3 $75.79   5.549%   $79.9956   $80.00   $80.00   $80.00  
  Purchase #4 $110.40   8.498%   $119.7818   $119.78   $119.80   $119.80  
  Purchase #5 $74.62   6.241%   $79.277   $79.28   $79.30   $79.30  
  Purchase #6 $243.89   8.195%   $263.8768   $263.88   $263.90   $263.90  
  Purchase #7 $24.25   8.418%   $26.2914   $26.29   $26.30   $26.30  
  7 purchase totals = $696.76       $752.9937   $753.00   $753.05   $753.10