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 $198.39   8.480%   $215.2135   $215.21   $215.20   $215.20  
  Purchase #2 $169.50   4.334%   $176.8461   $176.85   $176.85   $176.80  
  Purchase #3 $203.79   13.298%   $230.89   $230.89   $230.90   $230.90  
  Purchase #4 $55.49   5.862%   $58.7428   $58.74   $58.75   $58.70  
  Purchase #5 $24.93   6.515%   $26.5542   $26.55   $26.55   $26.60  
  Purchase #6 $56.51   4.143%   $58.8512   $58.85   $58.85   $58.90  
  Purchase #7 $135.61   5.813%   $143.493   $143.49   $143.50   $143.50  
  7 purchase totals = $844.22       $910.5908   $910.58   $910.60   $910.60