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 $153.82   6.648%   $164.046   $164.05   $164.05   $164.00  
  Purchase #2 $31.39   12.152%   $35.2045   $35.20   $35.20   $35.20  
  Purchase #3 $131.82   8.536%   $143.0722   $143.07   $143.05   $143.10  
  Purchase #4 $153.96   5.133%   $161.8628   $161.86   $161.85   $161.90  
  Purchase #5 $240.31   11.835%   $268.7507   $268.75   $268.75   $268.80  
  Purchase #6 $155.67   13.549%   $176.7617   $176.76   $176.75   $176.80  
  Purchase #7 $71.82   12.307%   $80.6589   $80.66   $80.65   $80.70  
  7 purchase totals = $938.79       $1,030.3568   $1,030.35   $1,030.30   $1,030.50