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 $83.86   8.761%   $91.207   $91.21   $91.20   $91.20  
  Purchase #2 $163.73   10.398%   $180.7546   $180.75   $180.75   $180.80  
  Purchase #3 $239.81   10.615%   $265.2658   $265.27   $265.25   $265.30  
  Purchase #4 $85.61   11.771%   $95.6872   $95.69   $95.70   $95.70  
  Purchase #5 $86.39   8.598%   $93.8178   $93.82   $93.80   $93.80  
  Purchase #6 $182.52   11.249%   $203.0517   $203.05   $203.05   $203.10  
  Purchase #7 $172.67   7.481%   $185.5874   $185.59   $185.60   $185.60  
  7 purchase totals = $1,014.59       $1,115.3715   $1,115.38   $1,115.35   $1,115.50