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 $76.53   9.419%   $83.7384   $83.74   $83.75   $83.70  
  Purchase #2 $25.94   10.246%   $28.5978   $28.60   $28.60   $28.60  
  Purchase #3 $69.92   11.131%   $77.7028   $77.70   $77.70   $77.70  
  Purchase #4 $223.28   5.314%   $235.1451   $235.15   $235.15   $235.10  
  Purchase #5 $71.53   4.373%   $74.658   $74.66   $74.65   $74.70  
  Purchase #6 $215.94   6.629%   $230.2547   $230.25   $230.25   $230.30  
  Purchase #7 $129.87   6.866%   $138.7869   $138.79   $138.80   $138.80  
  7 purchase totals = $813.01       $868.8837   $868.89   $868.90   $868.90