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 $56.52   10.131%   $62.246   $62.25   $62.25   $62.20  
  Purchase #2 $43.60   8.556%   $47.3304   $47.33   $47.35   $47.30  
  Purchase #3 $80.39   12.221%   $90.2145   $90.21   $90.20   $90.20  
  Purchase #4 $232.96   13.465%   $264.3281   $264.33   $264.35   $264.30  
  Purchase #5 $155.45   6.757%   $165.9538   $165.95   $165.95   $166.00  
  Purchase #6 $29.74   13.310%   $33.6984   $33.70   $33.70   $33.70  
  Purchase #7 $167.93   8.531%   $182.2561   $182.26   $182.25   $182.30  
  7 purchase totals = $766.59       $846.0273   $846.03   $846.05   $846.00