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 $67.29   13.436%   $76.3311   $76.33   $76.35   $76.30  
  Purchase #2 $161.50   5.752%   $170.7895   $170.79   $170.80   $170.80  
  Purchase #3 $168.35   5.283%   $177.2439   $177.24   $177.25   $177.20  
  Purchase #4 $159.64   3.827%   $165.7494   $165.75   $165.75   $165.70  
  Purchase #5 $75.86   12.293%   $85.1855   $85.19   $85.20   $85.20  
  Purchase #6 $176.40   3.810%   $183.1208   $183.12   $183.10   $183.10  
  Purchase #7 $8.52   12.528%   $9.5874   $9.59   $9.60   $9.60  
  7 purchase totals = $817.56       $868.0076   $868.01   $868.05   $867.90