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 $192.27   11.451%   $214.2868   $214.29   $214.30   $214.30  
  Purchase #2 $37.57   10.777%   $41.6189   $41.62   $41.60   $41.60  
  Purchase #3 $134.33   12.151%   $150.6524   $150.65   $150.65   $150.70  
  Purchase #4 $105.93   10.135%   $116.666   $116.67   $116.65   $116.70  
  Purchase #5 $36.28   8.654%   $39.4197   $39.42   $39.40   $39.40  
  Purchase #6 $165.38   8.613%   $179.6242   $179.62   $179.60   $179.60  
  Purchase #7 $166.51   4.112%   $173.3569   $173.36   $173.35   $173.40  
  7 purchase totals = $838.27       $915.6249   $915.63   $915.55   $915.70