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 $56.86   5.124%   $59.7735   $59.77   $59.75   $59.80  
  Purchase #2 $248.60   13.838%   $283.0013   $283.00   $283.00   $283.00  
  Purchase #3 $103.94   3.467%   $107.5436   $107.54   $107.55   $107.50  
  Purchase #4 $187.96   5.147%   $197.6343   $197.63   $197.65   $197.60  
  Purchase #5 $5.59   13.330%   $6.3351   $6.34   $6.35   $6.30  
  Purchase #6 $209.59   12.335%   $235.4429   $235.44   $235.45   $235.40  
  Purchase #7 $150.76   7.504%   $162.073   $162.07   $162.05   $162.10  
  7 purchase totals = $963.30       $1,051.8037   $1,051.79   $1,051.80   $1,051.70