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 $41.98   4.478%   $43.8599   $43.86   $43.85   $43.90  
  Purchase #2 $162.92   12.753%   $183.6972   $183.70   $183.70   $183.70  
  Purchase #3 $6.35   4.546%   $6.6387   $6.64   $6.65   $6.60  
  Purchase #4 $149.58   8.472%   $162.2524   $162.25   $162.25   $162.30  
  Purchase #5 $113.68   11.330%   $126.5599   $126.56   $126.55   $126.60  
  Purchase #6 $76.40   10.834%   $84.6772   $84.68   $84.70   $84.70  
  Purchase #7 $222.87   5.717%   $235.6115   $235.61   $235.60   $235.60  
  7 purchase totals = $773.78       $843.2968   $843.30   $843.30   $843.40