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 $219.31   13.119%   $248.0813   $248.08   $248.10   $248.10  
  Purchase #2 $56.42   9.248%   $61.6377   $61.64   $61.65   $61.60  
  Purchase #3 $156.90   6.499%   $167.0969   $167.10   $167.10   $167.10  
  Purchase #4 $198.71   10.410%   $219.3957   $219.40   $219.40   $219.40  
  Purchase #5 $125.50   7.357%   $134.733   $134.73   $134.75   $134.70  
  Purchase #6 $53.29   8.459%   $57.7978   $57.80   $57.80   $57.80  
  Purchase #7 $132.27   6.866%   $141.3517   $141.35   $141.35   $141.40  
  7 purchase totals = $942.40       $1,030.0941   $1,030.10   $1,030.15   $1,030.10