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 $185.44   8.179%   $200.6071   $200.61   $200.60   $200.60  
  Purchase #2 $53.50   10.311%   $59.0164   $59.02   $59.00   $59.00  
  Purchase #3 $230.65   7.385%   $247.6835   $247.68   $247.70   $247.70  
  Purchase #4 $68.99   9.462%   $75.5178   $75.52   $75.50   $75.50  
  Purchase #5 $24.40   8.659%   $26.5128   $26.51   $26.50   $26.50  
  Purchase #6 $242.27   8.305%   $262.3905   $262.39   $262.40   $262.40  
  Purchase #7 $197.85   7.135%   $211.9666   $211.97   $211.95   $212.00  
  7 purchase totals = $1,003.10       $1,083.6947   $1,083.70   $1,083.65   $1,083.70