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 $87.65   8.395%   $95.0082   $95.01   $95.00   $95.00  
  Purchase #2 $82.31   5.283%   $86.6584   $86.66   $86.65   $86.70  
  Purchase #3 $191.51   3.246%   $197.7264   $197.73   $197.75   $197.70  
  Purchase #4 $54.67   5.263%   $57.5473   $57.55   $57.55   $57.50  
  Purchase #5 $11.39   4.408%   $11.8921   $11.89   $11.90   $11.90  
  Purchase #6 $80.77   7.810%   $87.0781   $87.08   $87.10   $87.10  
  Purchase #7 $224.30   13.318%   $254.1723   $254.17   $254.15   $254.20  
  7 purchase totals = $732.60       $790.0828   $790.09   $790.10   $790.10