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 $116.87   8.813%   $127.1698   $127.17   $127.15   $127.20  
  Purchase #2 $124.78   5.158%   $131.2162   $131.22   $131.20   $131.20  
  Purchase #3 $181.29   10.845%   $200.9509   $200.95   $200.95   $201.00  
  Purchase #4 $126.55   7.731%   $136.3336   $136.33   $136.35   $136.30  
  Purchase #5 $118.55   12.642%   $133.5371   $133.54   $133.55   $133.50  
  Purchase #6 $219.55   6.769%   $234.4113   $234.41   $234.40   $234.40  
  Purchase #7 $12.88   4.117%   $13.4103   $13.41   $13.40   $13.40  
  7 purchase totals = $900.47       $977.0292   $977.03   $977.00   $977.00