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 $54.96   5.520%   $57.9938   $57.99   $58.00   $58.00  
  Purchase #2 $197.97   5.351%   $208.5634   $208.56   $208.55   $208.60  
  Purchase #3 $243.51   5.407%   $256.6766   $256.68   $256.70   $256.70  
  Purchase #4 $165.98   9.542%   $181.8178   $181.82   $181.80   $181.80  
  Purchase #5 $81.54   7.795%   $87.896   $87.90   $87.90   $87.90  
  Purchase #6 $231.78   13.806%   $263.7795   $263.78   $263.80   $263.80  
  Purchase #7 $95.61   9.495%   $104.6882   $104.69   $104.70   $104.70  
  7 purchase totals = $1,071.35       $1,161.4153   $1,161.42   $1,161.45   $1,161.50