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 $226.31   8.240%   $244.9579   $244.96   $244.95   $245.00  
  Purchase #2 $126.48   7.513%   $135.9824   $135.98   $136.00   $136.00  
  Purchase #3 $241.45   8.183%   $261.2079   $261.21   $261.20   $261.20  
  Purchase #4 $52.28   3.356%   $54.0345   $54.03   $54.05   $54.00  
  Purchase #5 $185.62   4.276%   $193.5571   $193.56   $193.55   $193.60  
  Purchase #6 $240.78   11.121%   $267.5571   $267.56   $267.55   $267.60  
  Purchase #7 $135.30   7.463%   $145.3974   $145.40   $145.40   $145.40  
  7 purchase totals = $1,208.22       $1,302.6943   $1,302.70   $1,302.70   $1,302.80