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 $55.71   13.135%   $63.0275   $63.03   $63.05   $63.00  
  Purchase #2 $120.28   5.484%   $126.8762   $126.88   $126.90   $126.90  
  Purchase #3 $103.94   13.582%   $118.0571   $118.06   $118.05   $118.10  
  Purchase #4 $237.53   8.653%   $258.0835   $258.08   $258.10   $258.10  
  Purchase #5 $140.91   8.685%   $153.148   $153.15   $153.15   $153.10  
  Purchase #6 $216.30   6.110%   $229.5159   $229.52   $229.50   $229.50  
  Purchase #7 $63.40   7.739%   $68.3065   $68.31   $68.30   $68.30  
  7 purchase totals = $938.07       $1,017.0147   $1,017.03   $1,017.05   $1,017.00