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 $60.53   10.420%   $66.8372   $66.84   $66.85   $66.80  
  Purchase #2 $82.80   6.228%   $87.9568   $87.96   $87.95   $88.00  
  Purchase #3 $181.95   11.587%   $203.0325   $203.03   $203.05   $203.00  
  Purchase #4 $84.68   10.120%   $93.2496   $93.25   $93.25   $93.20  
  Purchase #5 $185.83   3.346%   $192.0479   $192.05   $192.05   $192.00  
  Purchase #6 $200.59   6.869%   $214.3685   $214.37   $214.35   $214.40  
  Purchase #7 $170.71   12.176%   $191.4956   $191.50   $191.50   $191.50  
  7 purchase totals = $967.09       $1,048.9881   $1,049.00   $1,049.00   $1,048.90