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 $74.78   13.631%   $84.9733   $84.97   $84.95   $85.00  
  Purchase #2 $174.84   4.856%   $183.3302   $183.33   $183.35   $183.30  
  Purchase #3 $131.63   7.844%   $141.9551   $141.96   $141.95   $142.00  
  Purchase #4 $79.98   5.814%   $84.63   $84.63   $84.65   $84.60  
  Purchase #5 $231.86   3.234%   $239.3584   $239.36   $239.35   $239.40  
  Purchase #6 $187.25   7.485%   $201.2657   $201.27   $201.25   $201.30  
  Purchase #7 $70.67   6.241%   $75.0805   $75.08   $75.10   $75.10  
  7 purchase totals = $951.01       $1,010.5932   $1,010.60   $1,010.60   $1,010.70