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 $215.47   3.605%   $223.2377   $223.24   $223.25   $223.20  
  Purchase #2 $159.67   13.761%   $181.6422   $181.64   $181.65   $181.60  
  Purchase #3 $34.39   6.528%   $36.635   $36.64   $36.65   $36.60  
  Purchase #4 $173.89   10.451%   $192.0632   $192.06   $192.05   $192.10  
  Purchase #5 $147.29   9.695%   $161.5698   $161.57   $161.55   $161.60  
  Purchase #6 $169.81   10.188%   $187.1102   $187.11   $187.10   $187.10  
  Purchase #7 $37.52   5.317%   $39.5149   $39.51   $39.50   $39.50  
  7 purchase totals = $938.04       $1,021.7730   $1,021.77   $1,021.75   $1,021.70