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 $204.37   5.755%   $216.1315   $216.13   $216.15   $216.10  
  Purchase #2 $147.91   8.870%   $161.0296   $161.03   $161.05   $161.00  
  Purchase #3 $226.52   4.684%   $237.1302   $237.13   $237.15   $237.10  
  Purchase #4 $119.95   6.356%   $127.574   $127.57   $127.55   $127.60  
  Purchase #5 $36.50   13.780%   $41.5297   $41.53   $41.55   $41.50  
  Purchase #6 $215.77   13.522%   $244.9464   $244.95   $244.95   $244.90  
  Purchase #7 $240.44   11.407%   $267.867   $267.87   $267.85   $267.90  
  7 purchase totals = $1,191.46       $1,296.2084   $1,296.21   $1,296.25   $1,296.10