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 $29.80   8.645%   $32.3762   $32.38   $32.40   $32.40  
  Purchase #2 $174.85   9.683%   $191.7807   $191.78   $191.80   $191.80  
  Purchase #3 $160.42   5.662%   $169.503   $169.50   $169.50   $169.50  
  Purchase #4 $111.45   8.297%   $120.697   $120.70   $120.70   $120.70  
  Purchase #5 $48.82   8.685%   $53.06   $53.06   $53.05   $53.10  
  Purchase #6 $241.49   5.633%   $255.0931   $255.09   $255.10   $255.10  
  Purchase #7 $124.46   6.352%   $132.3657   $132.37   $132.35   $132.40  
  7 purchase totals = $891.29       $954.8757   $954.88   $954.90   $955.00