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 $165.94   13.263%   $187.9486   $187.95   $187.95   $187.90  
  Purchase #2 $21.87   10.491%   $24.1644   $24.16   $24.15   $24.20  
  Purchase #3 $65.97   8.495%   $71.5742   $71.57   $71.55   $71.60  
  Purchase #4 $34.64   6.541%   $36.9058   $36.91   $36.90   $36.90  
  Purchase #5 $57.39   4.747%   $60.1143   $60.11   $60.10   $60.10  
  Purchase #6 $204.97   11.420%   $228.3776   $228.38   $228.40   $228.40  
  Purchase #7 $126.69   11.243%   $140.9338   $140.93   $140.95   $140.90  
  7 purchase totals = $677.47       $750.0187   $750.01   $750.00   $750.00