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 $50.73   13.537%   $57.5973   $57.60   $57.60   $57.60  
  Purchase #2 $171.50   6.419%   $182.5086   $182.51   $182.50   $182.50  
  Purchase #3 $211.56   6.787%   $225.9186   $225.92   $225.90   $225.90  
  Purchase #4 $177.26   9.199%   $193.5661   $193.57   $193.55   $193.60  
  Purchase #5 $119.72   13.124%   $135.4321   $135.43   $135.45   $135.40  
  Purchase #6 $142.28   9.109%   $155.2403   $155.24   $155.25   $155.20  
  Purchase #7 $77.41   5.721%   $81.8386   $81.84   $81.85   $81.80  
  7 purchase totals = $950.46       $1,032.1016   $1,032.11   $1,032.10   $1,032.00