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 $64.85   12.716%   $73.0963   $73.10   $73.10   $73.10  
  Purchase #2 $192.55   8.820%   $209.5329   $209.53   $209.55   $209.50  
  Purchase #3 $51.67   12.361%   $58.0569   $58.06   $58.05   $58.10  
  Purchase #4 $151.89   11.506%   $169.3665   $169.37   $169.35   $169.40  
  Purchase #5 $52.60   8.740%   $57.1972   $57.20   $57.20   $57.20  
  Purchase #6 $241.72   5.604%   $255.266   $255.27   $255.25   $255.30  
  Purchase #7 $109.30   13.170%   $123.6948   $123.69   $123.70   $123.70  
  7 purchase totals = $864.58       $946.2106   $946.22   $946.20   $946.30