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 $161.43   7.648%   $173.7762   $173.78   $173.80   $173.80  
  Purchase #2 $73.38   12.739%   $82.7279   $82.73   $82.75   $82.70  
  Purchase #3 $127.90   12.644%   $144.0717   $144.07   $144.05   $144.10  
  Purchase #4 $177.71   6.727%   $189.6646   $189.66   $189.65   $189.70  
  Purchase #5 $118.62   5.656%   $125.3291   $125.33   $125.35   $125.30  
  Purchase #6 $243.30   10.715%   $269.3696   $269.37   $269.35   $269.40  
  Purchase #7 $44.65   13.648%   $50.7438   $50.74   $50.75   $50.70  
  7 purchase totals = $946.99       $1,035.6829   $1,035.68   $1,035.70   $1,035.70