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 $75.59   10.237%   $83.3281   $83.33   $83.35   $83.30  
  Purchase #2 $114.92   10.821%   $127.3555   $127.36   $127.35   $127.40  
  Purchase #3 $118.46   10.306%   $130.6685   $130.67   $130.65   $130.70  
  Purchase #4 $181.52   13.624%   $206.2503   $206.25   $206.25   $206.30  
  Purchase #5 $233.95   11.237%   $260.239   $260.24   $260.25   $260.20  
  Purchase #6 $75.35   4.251%   $78.5531   $78.55   $78.55   $78.60  
  Purchase #7 $176.27   6.422%   $187.5901   $187.59   $187.60   $187.60  
  7 purchase totals = $976.06       $1,073.9846   $1,073.99   $1,074.00   $1,074.10