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 $23.86   10.461%   $26.356   $26.36   $26.35   $26.40  
  Purchase #2 $39.70   3.389%   $41.0454   $41.05   $41.05   $41.00  
  Purchase #3 $173.54   13.564%   $197.079   $197.08   $197.10   $197.10  
  Purchase #4 $237.29   5.619%   $250.6233   $250.62   $250.60   $250.60  
  Purchase #5 $138.97   9.260%   $151.8386   $151.84   $151.85   $151.80  
  Purchase #6 $110.70   9.778%   $121.5242   $121.52   $121.50   $121.50  
  Purchase #7 $124.86   10.338%   $137.768   $137.77   $137.75   $137.80  
  7 purchase totals = $848.92       $926.2345   $926.24   $926.20   $926.20