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 $73.81   13.772%   $83.9751   $83.98   $84.00   $84.00  
  Purchase #2 $119.87   11.687%   $133.8792   $133.88   $133.90   $133.90  
  Purchase #3 $24.97   3.649%   $25.8812   $25.88   $25.90   $25.90  
  Purchase #4 $201.52   7.658%   $216.9524   $216.95   $216.95   $217.00  
  Purchase #5 $145.85   7.395%   $156.6356   $156.64   $156.65   $156.60  
  Purchase #6 $204.44   8.136%   $221.0732   $221.07   $221.05   $221.10  
  Purchase #7 $226.68   5.485%   $239.1134   $239.11   $239.10   $239.10  
  7 purchase totals = $997.14       $1,077.5101   $1,077.51   $1,077.55   $1,077.60