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 $68.82   5.706%   $72.7469   $72.75   $72.75   $72.70  
  Purchase #2 $227.90   13.217%   $258.0215   $258.02   $258.00   $258.00  
  Purchase #3 $148.90   7.793%   $160.5038   $160.50   $160.50   $160.50  
  Purchase #4 $24.49   6.384%   $26.0534   $26.05   $26.05   $26.10  
  Purchase #5 $71.29   12.490%   $80.1941   $80.19   $80.20   $80.20  
  Purchase #6 $10.86   4.735%   $11.3742   $11.37   $11.35   $11.40  
  Purchase #7 $130.97   8.184%   $141.6886   $141.69   $141.70   $141.70  
  7 purchase totals = $683.23       $750.5825   $750.57   $750.55   $750.60