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 $52.97   7.609%   $57.0005   $57.00   $57.00   $57.00  
  Purchase #2 $225.87   10.273%   $249.0736   $249.07   $249.05   $249.10  
  Purchase #3 $56.74   5.689%   $59.9679   $59.97   $59.95   $60.00  
  Purchase #4 $217.40   6.483%   $231.494   $231.49   $231.50   $231.50  
  Purchase #5 $219.73   10.625%   $243.0763   $243.08   $243.10   $243.10  
  Purchase #6 $237.42   6.723%   $253.3817   $253.38   $253.40   $253.40  
  Purchase #7 $248.61   10.346%   $274.3312   $274.33   $274.35   $274.30  
  7 purchase totals = $1,258.74       $1,368.3252   $1,368.32   $1,368.35   $1,368.40