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 $240.51   11.344%   $267.7935   $267.79   $267.80   $267.80  
  Purchase #2 $62.89   11.477%   $70.1079   $70.11   $70.10   $70.10  
  Purchase #3 $99.46   3.642%   $103.0823   $103.08   $103.10   $103.10  
  Purchase #4 $248.51   11.310%   $276.6165   $276.62   $276.60   $276.60  
  Purchase #5 $157.27   7.468%   $169.0149   $169.01   $169.00   $169.00  
  Purchase #6 $220.87   10.221%   $243.4451   $243.45   $243.45   $243.40  
  Purchase #7 $60.94   4.491%   $63.6768   $63.68   $63.70   $63.70  
  7 purchase totals = $1,090.45       $1,193.7370   $1,193.74   $1,193.75   $1,193.70