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 $96.62   7.263%   $103.6375   $103.64   $103.65   $103.60  
  Purchase #2 $182.47   4.721%   $191.0844   $191.08   $191.10   $191.10  
  Purchase #3 $5.77   8.566%   $6.2643   $6.26   $6.25   $6.30  
  Purchase #4 $177.38   13.611%   $201.5232   $201.52   $201.50   $201.50  
  Purchase #5 $150.84   11.287%   $167.8653   $167.87   $167.85   $167.90  
  Purchase #6 $70.92   9.413%   $77.5957   $77.60   $77.60   $77.60  
  Purchase #7 $57.34   12.261%   $64.3705   $64.37   $64.35   $64.40  
  7 purchase totals = $741.34       $812.3409   $812.34   $812.30   $812.40