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 $61.44   12.271%   $68.9793   $68.98   $69.00   $69.00  
  Purchase #2 $63.52   13.270%   $71.9491   $71.95   $71.95   $71.90  
  Purchase #3 $46.34   11.666%   $51.746   $51.75   $51.75   $51.70  
  Purchase #4 $156.33   11.608%   $174.4768   $174.48   $174.50   $174.50  
  Purchase #5 $44.85   12.182%   $50.3136   $50.31   $50.30   $50.30  
  Purchase #6 $98.71   6.113%   $104.7441   $104.74   $104.75   $104.70  
  Purchase #7 $179.77   6.136%   $190.8007   $190.80   $190.80   $190.80  
  7 purchase totals = $650.96       $713.0096   $713.01   $713.05   $712.90