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 $227.89   3.809%   $236.5703   $236.57   $236.55   $236.60  
  Purchase #2 $162.91   3.846%   $169.1755   $169.18   $169.20   $169.20  
  Purchase #3 $62.58   7.365%   $67.189   $67.19   $67.20   $67.20  
  Purchase #4 $183.68   10.161%   $202.3437   $202.34   $202.35   $202.30  
  Purchase #5 $194.38   11.224%   $216.1972   $216.20   $216.20   $216.20  
  Purchase #6 $33.34   7.335%   $35.7855   $35.79   $35.80   $35.80  
  Purchase #7 $70.86   5.475%   $74.7396   $74.74   $74.75   $74.70  
  7 purchase totals = $935.64       $1,002.0008   $1,002.01   $1,002.05   $1,002.00