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 $29.47   13.819%   $33.5425   $33.54   $33.55   $33.50  
  Purchase #2 $233.85   8.816%   $254.4662   $254.47   $254.45   $254.50  
  Purchase #3 $141.77   3.872%   $147.2593   $147.26   $147.25   $147.30  
  Purchase #4 $203.55   8.293%   $220.4304   $220.43   $220.45   $220.40  
  Purchase #5 $129.29   7.243%   $138.6545   $138.65   $138.65   $138.70  
  Purchase #6 $168.27   6.691%   $179.5289   $179.53   $179.55   $179.50  
  Purchase #7 $240.46   6.186%   $255.3349   $255.33   $255.35   $255.30  
  7 purchase totals = $1,146.66       $1,229.2167   $1,229.21   $1,229.25   $1,229.20