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 $111.92   11.743%   $125.0628   $125.06   $125.05   $125.10  
  Purchase #2 $183.26   9.572%   $200.8016   $200.80   $200.80   $200.80  
  Purchase #3 $38.74   13.420%   $43.9389   $43.94   $43.95   $43.90  
  Purchase #4 $216.68   8.586%   $235.2841   $235.28   $235.30   $235.30  
  Purchase #5 $116.72   9.427%   $127.7232   $127.72   $127.70   $127.70  
  Purchase #6 $183.63   5.386%   $193.5203   $193.52   $193.50   $193.50  
  Purchase #7 $116.77   13.103%   $132.0704   $132.07   $132.05   $132.10  
  7 purchase totals = $967.72       $1,058.4013   $1,058.39   $1,058.35   $1,058.40