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 $171.29   13.451%   $194.3302   $194.33   $194.35   $194.30  
  Purchase #2 $211.63   7.509%   $227.5213   $227.52   $227.50   $227.50  
  Purchase #3 $169.33   10.704%   $187.4551   $187.46   $187.45   $187.50  
  Purchase #4 $170.73   8.145%   $184.636   $184.64   $184.65   $184.60  
  Purchase #5 $16.74   6.541%   $17.835   $17.84   $17.85   $17.80  
  Purchase #6 $128.78   9.281%   $140.7321   $140.73   $140.75   $140.70  
  Purchase #7 $236.69   6.643%   $252.4133   $252.41   $252.40   $252.40  
  7 purchase totals = $1,105.19       $1,204.9230   $1,204.93   $1,204.95   $1,204.80