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 $182.35   12.255%   $204.697   $204.70   $204.70   $204.70  
  Purchase #2 $32.86   5.404%   $34.6358   $34.64   $34.65   $34.60  
  Purchase #3 $160.49   13.568%   $182.2653   $182.27   $182.25   $182.30  
  Purchase #4 $76.54   12.199%   $85.8771   $85.88   $85.90   $85.90  
  Purchase #5 $169.75   12.541%   $191.0383   $191.04   $191.05   $191.00  
  Purchase #6 $247.95   7.160%   $265.7032   $265.70   $265.70   $265.70  
  Purchase #7 $198.65   6.472%   $211.5066   $211.51   $211.50   $211.50  
  7 purchase totals = $1,068.59       $1,175.7233   $1,175.74   $1,175.75   $1,175.70