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 $173.80   11.868%   $194.4266   $194.43   $194.45   $194.40  
  Purchase #2 $36.57   4.113%   $38.0741   $38.07   $38.05   $38.10  
  Purchase #3 $91.69   4.196%   $95.5373   $95.54   $95.55   $95.50  
  Purchase #4 $205.61   12.651%   $231.6217   $231.62   $231.60   $231.60  
  Purchase #5 $67.47   13.416%   $76.5218   $76.52   $76.50   $76.50  
  Purchase #6 $112.96   5.686%   $119.3829   $119.38   $119.40   $119.40  
  Purchase #7 $245.33   11.360%   $273.1995   $273.20   $273.20   $273.20  
  7 purchase totals = $933.43       $1,028.7639   $1,028.76   $1,028.75   $1,028.70