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 $76.75   10.467%   $84.7834   $84.78   $84.80   $84.80  
  Purchase #2 $173.36   4.826%   $181.7264   $181.73   $181.75   $181.70  
  Purchase #3 $80.49   8.549%   $87.3711   $87.37   $87.35   $87.40  
  Purchase #4 $193.96   11.655%   $216.566   $216.57   $216.55   $216.60  
  Purchase #5 $197.92   4.152%   $206.1376   $206.14   $206.15   $206.10  
  Purchase #6 $202.38   5.781%   $214.0796   $214.08   $214.10   $214.10  
  Purchase #7 $32.73   8.159%   $35.4004   $35.40   $35.40   $35.40  
  7 purchase totals = $957.59       $1,026.0645   $1,026.07   $1,026.10   $1,026.10