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 $69.86   9.537%   $76.5225   $76.52   $76.50   $76.50  
  Purchase #2 $79.66   6.392%   $84.7519   $84.75   $84.75   $84.80  
  Purchase #3 $202.49   4.578%   $211.76   $211.76   $211.75   $211.80  
  Purchase #4 $142.95   7.460%   $153.6141   $153.61   $153.60   $153.60  
  Purchase #5 $153.85   10.630%   $170.2043   $170.20   $170.20   $170.20  
  Purchase #6 $55.65   4.804%   $58.3234   $58.32   $58.30   $58.30  
  Purchase #7 $7.29   4.109%   $7.5895   $7.59   $7.60   $7.60  
  7 purchase totals = $711.75       $762.7657   $762.75   $762.70   $762.80