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 $113.68   9.248%   $124.1931   $124.19   $124.20   $124.20  
  Purchase #2 $234.62   8.177%   $253.8049   $253.80   $253.80   $253.80  
  Purchase #3 $179.25   9.390%   $196.0816   $196.08   $196.10   $196.10  
  Purchase #4 $25.97   7.737%   $27.9793   $27.98   $28.00   $28.00  
  Purchase #5 $64.25   6.814%   $68.628   $68.63   $68.65   $68.60  
  Purchase #6 $154.67   12.327%   $173.7362   $173.74   $173.75   $173.70  
  Purchase #7 $167.76   6.446%   $178.5738   $178.57   $178.55   $178.60  
  7 purchase totals = $940.20       $1,022.9969   $1,022.99   $1,023.05   $1,023.00