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 $99.34   12.178%   $111.4376   $111.44   $111.45   $111.40  
  Purchase #2 $246.98   6.174%   $262.2285   $262.23   $262.25   $262.20  
  Purchase #3 $53.51   4.853%   $56.1068   $56.11   $56.10   $56.10  
  Purchase #4 $119.27   13.190%   $135.0017   $135.00   $135.00   $135.00  
  Purchase #5 $25.96   11.618%   $28.976   $28.98   $29.00   $29.00  
  Purchase #6 $248.60   11.417%   $276.9827   $276.98   $277.00   $277.00  
  Purchase #7 $201.87   6.202%   $214.39   $214.39   $214.40   $214.40  
  7 purchase totals = $995.53       $1,085.1233   $1,085.13   $1,085.20   $1,085.10