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 $69.48   5.578%   $73.3556   $73.36   $73.35   $73.40  
  Purchase #2 $149.26   5.441%   $157.3812   $157.38   $157.40   $157.40  
  Purchase #3 $140.35   7.574%   $150.9801   $150.98   $151.00   $151.00  
  Purchase #4 $38.53   7.363%   $41.367   $41.37   $41.35   $41.40  
  Purchase #5 $222.29   5.641%   $234.8294   $234.83   $234.85   $234.80  
  Purchase #6 $172.37   9.378%   $188.5349   $188.53   $188.55   $188.50  
  Purchase #7 $221.34   10.842%   $245.3377   $245.34   $245.35   $245.30  
  7 purchase totals = $1,013.62       $1,091.7859   $1,091.79   $1,091.85   $1,091.80