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 $63.42   4.367%   $66.1896   $66.19   $66.20   $66.20  
  Purchase #2 $206.33   11.628%   $230.3221   $230.32   $230.30   $230.30  
  Purchase #3 $78.83   11.364%   $87.7882   $87.79   $87.80   $87.80  
  Purchase #4 $243.43   12.443%   $273.72   $273.72   $273.70   $273.70  
  Purchase #5 $15.80   4.184%   $16.4611   $16.46   $16.45   $16.50  
  Purchase #6 $68.27   6.352%   $72.6065   $72.61   $72.60   $72.60  
  Purchase #7 $174.70   11.196%   $194.2594   $194.26   $194.25   $194.30  
  7 purchase totals = $850.78       $941.3469   $941.35   $941.30   $941.40