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 $98.47   13.465%   $111.729   $111.73   $111.75   $111.70  
  Purchase #2 $60.38   13.250%   $68.3804   $68.38   $68.40   $68.40  
  Purchase #3 $162.90   13.373%   $184.6846   $184.68   $184.70   $184.70  
  Purchase #4 $18.49   8.329%   $20.03   $20.03   $20.05   $20.00  
  Purchase #5 $87.56   12.565%   $98.5619   $98.56   $98.55   $98.60  
  Purchase #6 $39.77   8.408%   $43.1139   $43.11   $43.10   $43.10  
  Purchase #7 $36.42   8.821%   $39.6326   $39.63   $39.65   $39.60  
  7 purchase totals = $503.99       $566.1324   $566.12   $566.20   $566.10