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 $98.25   11.225%   $109.2786   $109.28   $109.30   $109.30  
  Purchase #2 $214.97   9.157%   $234.6548   $234.65   $234.65   $234.70  
  Purchase #3 $45.87   13.818%   $52.2083   $52.21   $52.20   $52.20  
  Purchase #4 $189.53   6.357%   $201.5784   $201.58   $201.60   $201.60  
  Purchase #5 $165.33   5.682%   $174.7241   $174.72   $174.70   $174.70  
  Purchase #6 $36.52   10.828%   $40.4744   $40.47   $40.45   $40.50  
  Purchase #7 $216.38   11.497%   $241.2572   $241.26   $241.25   $241.30  
  7 purchase totals = $966.85       $1,054.1758   $1,054.17   $1,054.15   $1,054.30