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 $54.97   11.563%   $61.3262   $61.33   $61.35   $61.30  
  Purchase #2 $231.82   7.177%   $248.4577   $248.46   $248.45   $248.50  
  Purchase #3 $180.97   6.777%   $193.2343   $193.23   $193.25   $193.20  
  Purchase #4 $207.56   13.309%   $235.1842   $235.18   $235.20   $235.20  
  Purchase #5 $197.61   10.623%   $218.6021   $218.60   $218.60   $218.60  
  Purchase #6 $47.51   9.673%   $52.1056   $52.11   $52.10   $52.10  
  Purchase #7 $46.91   9.590%   $51.4087   $51.41   $51.40   $51.40  
  7 purchase totals = $967.35       $1,060.3188   $1,060.32   $1,060.35   $1,060.30