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 $71.84   4.791%   $75.2819   $75.28   $75.30   $75.30  
  Purchase #2 $57.41   11.219%   $63.8508   $63.85   $63.85   $63.90  
  Purchase #3 $19.99   8.826%   $21.7543   $21.75   $21.75   $21.80  
  Purchase #4 $142.32   6.106%   $151.0101   $151.01   $151.00   $151.00  
  Purchase #5 $171.37   4.621%   $179.289   $179.29   $179.30   $179.30  
  Purchase #6 $206.80   7.381%   $222.0639   $222.06   $222.05   $222.10  
  Purchase #7 $125.70   10.295%   $138.6408   $138.64   $138.65   $138.60  
  7 purchase totals = $795.43       $851.8908   $851.88   $851.90   $852.00