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 $61.34   8.559%   $66.5901   $66.59   $66.60   $66.60  
  Purchase #2 $245.42   8.488%   $266.2512   $266.25   $266.25   $266.30  
  Purchase #3 $249.67   3.645%   $258.7705   $258.77   $258.75   $258.80  
  Purchase #4 $184.65   3.811%   $191.687   $191.69   $191.70   $191.70  
  Purchase #5 $216.40   12.784%   $244.0646   $244.06   $244.05   $244.10  
  Purchase #6 $207.84   11.776%   $232.3152   $232.32   $232.30   $232.30  
  Purchase #7 $36.73   13.425%   $41.661   $41.66   $41.65   $41.70  
  7 purchase totals = $1,202.05       $1,301.3396   $1,301.34   $1,301.30   $1,301.50