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 $131.82   11.357%   $146.7908   $146.79   $146.80   $146.80  
  Purchase #2 $186.62   8.607%   $202.6824   $202.68   $202.70   $202.70  
  Purchase #3 $163.38   11.248%   $181.757   $181.76   $181.75   $181.80  
  Purchase #4 $66.81   9.789%   $73.35   $73.35   $73.35   $73.40  
  Purchase #5 $61.84   11.376%   $68.8749   $68.87   $68.85   $68.90  
  Purchase #6 $159.81   5.411%   $168.4573   $168.46   $168.45   $168.50  
  Purchase #7 $205.48   9.492%   $224.9842   $224.98   $225.00   $225.00  
  7 purchase totals = $975.76       $1,066.8966   $1,066.89   $1,066.90   $1,067.10