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 $88.35   6.552%   $94.1387   $94.14   $94.15   $94.10  
  Purchase #2 $235.78   7.158%   $252.6571   $252.66   $252.65   $252.70  
  Purchase #3 $151.65   9.599%   $166.2069   $166.21   $166.20   $166.20  
  Purchase #4 $248.37   6.244%   $263.8782   $263.88   $263.90   $263.90  
  Purchase #5 $26.59   6.467%   $28.3096   $28.31   $28.30   $28.30  
  Purchase #6 $120.63   7.604%   $129.8027   $129.80   $129.80   $129.80  
  Purchase #7 $133.37   13.742%   $151.6977   $151.70   $151.70   $151.70  
  7 purchase totals = $1,004.74       $1,086.6909   $1,086.70   $1,086.70   $1,086.70