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 $23.96   11.336%   $26.6761   $26.68   $26.70   $26.70  
  Purchase #2 $207.87   5.122%   $218.5171   $218.52   $218.50   $218.50  
  Purchase #3 $28.73   5.235%   $30.234   $30.23   $30.25   $30.20  
  Purchase #4 $234.34   8.624%   $254.5495   $254.55   $254.55   $254.50  
  Purchase #5 $228.92   11.787%   $255.9028   $255.90   $255.90   $255.90  
  Purchase #6 $59.62   4.170%   $62.1062   $62.11   $62.10   $62.10  
  Purchase #7 $189.82   6.739%   $202.612   $202.61   $202.60   $202.60  
  7 purchase totals = $973.26       $1,050.5977   $1,050.60   $1,050.60   $1,050.50