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 $52.69   11.348%   $58.6693   $58.67   $58.65   $58.70  
  Purchase #2 $50.39   3.628%   $52.2181   $52.22   $52.20   $52.20  
  Purchase #3 $237.94   12.364%   $267.3589   $267.36   $267.35   $267.40  
  Purchase #4 $237.67   4.636%   $248.6884   $248.69   $248.70   $248.70  
  Purchase #5 $53.38   9.666%   $58.5397   $58.54   $58.55   $58.50  
  Purchase #6 $46.47   10.465%   $51.3331   $51.33   $51.35   $51.30  
  Purchase #7 $22.30   12.142%   $25.0077   $25.01   $25.00   $25.00  
  7 purchase totals = $700.84       $761.8152   $761.82   $761.80   $761.80