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 $101.52   5.262%   $106.862   $106.86   $106.85   $106.90  
  Purchase #2 $68.39   7.194%   $73.31   $73.31   $73.30   $73.30  
  Purchase #3 $24.25   11.266%   $26.982   $26.98   $27.00   $27.00  
  Purchase #4 $106.76   11.439%   $118.9723   $118.97   $118.95   $119.00  
  Purchase #5 $84.91   4.349%   $88.6027   $88.60   $88.60   $88.60  
  Purchase #6 $222.87   8.385%   $241.5576   $241.56   $241.55   $241.60  
  Purchase #7 $182.52   6.113%   $193.6774   $193.68   $193.70   $193.70  
  7 purchase totals = $791.22       $849.9640   $849.96   $849.95   $850.10