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 $207.98   11.766%   $232.4509   $232.45   $232.45   $232.50  
  Purchase #2 $59.72   10.609%   $66.0557   $66.06   $66.05   $66.10  
  Purchase #3 $54.85   11.318%   $61.0579   $61.06   $61.05   $61.10  
  Purchase #4 $180.27   10.610%   $199.3966   $199.40   $199.40   $199.40  
  Purchase #5 $181.94   7.574%   $195.7201   $195.72   $195.70   $195.70  
  Purchase #6 $105.89   7.201%   $113.5151   $113.52   $113.50   $113.50  
  Purchase #7 $188.93   9.122%   $206.1642   $206.16   $206.15   $206.20  
  7 purchase totals = $979.58       $1,074.3605   $1,074.37   $1,074.30   $1,074.50