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 $228.25   8.333%   $247.2701   $247.27   $247.25   $247.30  
  Purchase #2 $150.27   10.601%   $166.2001   $166.20   $166.20   $166.20  
  Purchase #3 $156.56   11.431%   $174.4564   $174.46   $174.45   $174.50  
  Purchase #4 $115.49   11.282%   $128.5196   $128.52   $128.50   $128.50  
  Purchase #5 $78.52   9.780%   $86.1993   $86.20   $86.20   $86.20  
  Purchase #6 $124.65   11.426%   $138.8925   $138.89   $138.90   $138.90  
  Purchase #7 $77.43   7.187%   $82.9949   $82.99   $83.00   $83.00  
  7 purchase totals = $931.17       $1,024.5329   $1,024.53   $1,024.50   $1,024.60