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 $55.96   5.470%   $59.021   $59.02   $59.00   $59.00  
  Purchase #2 $199.55   4.492%   $208.5138   $208.51   $208.50   $208.50  
  Purchase #3 $151.30   6.775%   $161.5506   $161.55   $161.55   $161.60  
  Purchase #4 $193.26   12.244%   $216.9228   $216.92   $216.90   $216.90  
  Purchase #5 $118.86   4.231%   $123.889   $123.89   $123.90   $123.90  
  Purchase #6 $64.31   5.236%   $67.6773   $67.68   $67.70   $67.70  
  Purchase #7 $5.94   3.233%   $6.132   $6.13   $6.15   $6.10  
  7 purchase totals = $789.18       $843.7065   $843.70   $843.70   $843.70