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 $88.52   5.272%   $93.1868   $93.19   $93.20   $93.20  
  Purchase #2 $232.97   6.320%   $247.6937   $247.69   $247.70   $247.70  
  Purchase #3 $19.36   3.197%   $19.9789   $19.98   $20.00   $20.00  
  Purchase #4 $8.71   5.564%   $9.1946   $9.19   $9.20   $9.20  
  Purchase #5 $71.36   8.242%   $77.2415   $77.24   $77.25   $77.20  
  Purchase #6 $153.98   8.321%   $166.7927   $166.79   $166.80   $166.80  
  Purchase #7 $93.84   7.371%   $100.7569   $100.76   $100.75   $100.80  
  7 purchase totals = $668.74       $714.8451   $714.84   $714.90   $714.90