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 $152.46   7.357%   $163.6765   $163.68   $163.70   $163.70  
  Purchase #2 $97.62   3.498%   $101.0347   $101.03   $101.05   $101.00  
  Purchase #3 $12.95   3.853%   $13.449   $13.45   $13.45   $13.40  
  Purchase #4 $179.55   13.599%   $203.967   $203.97   $203.95   $204.00  
  Purchase #5 $48.57   8.427%   $52.663   $52.66   $52.65   $52.70  
  Purchase #6 $63.33   13.818%   $72.0809   $72.08   $72.10   $72.10  
  Purchase #7 $122.83   9.826%   $134.8993   $134.90   $134.90   $134.90  
  7 purchase totals = $677.31       $741.7704   $741.77   $741.80   $741.80