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 $105.62   13.147%   $119.5059   $119.51   $119.50   $119.50  
  Purchase #2 $223.63   7.341%   $240.0467   $240.05   $240.05   $240.00  
  Purchase #3 $212.64   8.231%   $230.1424   $230.14   $230.15   $230.10  
  Purchase #4 $22.42   7.351%   $24.0681   $24.07   $24.05   $24.10  
  Purchase #5 $160.86   9.851%   $176.7063   $176.71   $176.70   $176.70  
  Purchase #6 $189.58   12.643%   $213.5486   $213.55   $213.55   $213.50  
  Purchase #7 $24.68   10.790%   $27.343   $27.34   $27.35   $27.30  
  7 purchase totals = $939.43       $1,031.3610   $1,031.37   $1,031.35   $1,031.20