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 $32.95   10.118%   $36.2839   $36.28   $36.30   $36.30  
  Purchase #2 $168.54   13.469%   $191.2407   $191.24   $191.25   $191.20  
  Purchase #3 $190.94   7.294%   $204.8672   $204.87   $204.85   $204.90  
  Purchase #4 $63.32   9.237%   $69.1689   $69.17   $69.15   $69.20  
  Purchase #5 $92.74   6.432%   $98.705   $98.71   $98.70   $98.70  
  Purchase #6 $138.38   12.384%   $155.517   $155.52   $155.50   $155.50  
  Purchase #7 $140.90   8.490%   $152.8624   $152.86   $152.85   $152.90  
  7 purchase totals = $827.77       $908.6451   $908.65   $908.60   $908.70