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 $194.79   6.521%   $207.4923   $207.49   $207.50   $207.50  
  Purchase #2 $28.81   6.225%   $30.6034   $30.60   $30.60   $30.60  
  Purchase #3 $245.52   9.828%   $269.6497   $269.65   $269.65   $269.60  
  Purchase #4 $192.61   9.734%   $211.3587   $211.36   $211.35   $211.40  
  Purchase #5 $192.74   13.625%   $219.0008   $219.00   $219.00   $219.00  
  Purchase #6 $27.42   9.367%   $29.9884   $29.99   $30.00   $30.00  
  Purchase #7 $80.68   8.519%   $87.5531   $87.55   $87.55   $87.60  
  7 purchase totals = $962.57       $1,055.6464   $1,055.64   $1,055.65   $1,055.70