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 $195.38   13.636%   $222.022   $222.02   $222.00   $222.00  
  Purchase #2 $20.52   13.401%   $23.2699   $23.27   $23.25   $23.30  
  Purchase #3 $111.84   4.433%   $116.7979   $116.80   $116.80   $116.80  
  Purchase #4 $165.66   6.226%   $175.974   $175.97   $175.95   $176.00  
  Purchase #5 $26.33   6.422%   $28.0209   $28.02   $28.00   $28.00  
  Purchase #6 $74.67   7.436%   $80.2225   $80.22   $80.20   $80.20  
  Purchase #7 $211.66   7.268%   $227.0434   $227.04   $227.05   $227.00  
  7 purchase totals = $806.06       $873.3506   $873.34   $873.25   $873.30