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 $126.67   5.639%   $133.8129   $133.81   $133.80   $133.80  
  Purchase #2 $84.71   5.654%   $89.4995   $89.50   $89.50   $89.50  
  Purchase #3 $222.99   10.798%   $247.0685   $247.07   $247.05   $247.10  
  Purchase #4 $134.84   9.853%   $148.1258   $148.13   $148.15   $148.10  
  Purchase #5 $172.98   9.567%   $189.529   $189.53   $189.55   $189.50  
  Purchase #6 $52.88   3.488%   $54.7245   $54.72   $54.70   $54.70  
  Purchase #7 $52.29   12.660%   $58.9099   $58.91   $58.90   $58.90  
  7 purchase totals = $847.36       $921.6701   $921.67   $921.65   $921.60