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 $120.73   11.162%   $134.2059   $134.21   $134.20   $134.20  
  Purchase #2 $67.74   11.551%   $75.5646   $75.56   $75.55   $75.60  
  Purchase #3 $204.54   4.192%   $213.1143   $213.11   $213.10   $213.10  
  Purchase #4 $166.41   11.688%   $185.86   $185.86   $185.85   $185.90  
  Purchase #5 $178.97   7.258%   $191.9596   $191.96   $191.95   $192.00  
  Purchase #6 $238.55   11.198%   $265.2628   $265.26   $265.25   $265.30  
  Purchase #7 $192.64   6.864%   $205.8628   $205.86   $205.85   $205.90  
  7 purchase totals = $1,169.58       $1,271.8300   $1,271.82   $1,271.75   $1,272.00