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 $90.43   5.319%   $95.24   $95.24   $95.25   $95.20  
  Purchase #2 $145.42   3.541%   $150.5693   $150.57   $150.55   $150.60  
  Purchase #3 $6.55   10.530%   $7.2397   $7.24   $7.25   $7.20  
  Purchase #4 $13.81   9.107%   $15.0677   $15.07   $15.05   $15.10  
  Purchase #5 $65.71   10.337%   $72.5024   $72.50   $72.50   $72.50  
  Purchase #6 $223.92   5.506%   $236.249   $236.25   $236.25   $236.20  
  Purchase #7 $10.45   9.166%   $11.4078   $11.41   $11.40   $11.40  
  7 purchase totals = $556.29       $588.2759   $588.28   $588.25   $588.20