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 $185.48   6.783%   $198.0611   $198.06   $198.05   $198.10  
  Purchase #2 $103.74   3.222%   $107.0825   $107.08   $107.10   $107.10  
  Purchase #3 $84.41   5.271%   $88.8593   $88.86   $88.85   $88.90  
  Purchase #4 $48.96   5.150%   $51.4814   $51.48   $51.50   $51.50  
  Purchase #5 $183.91   11.680%   $205.3907   $205.39   $205.40   $205.40  
  Purchase #6 $213.91   5.797%   $226.3104   $226.31   $226.30   $226.30  
  Purchase #7 $138.97   7.355%   $149.1912   $149.19   $149.20   $149.20  
  7 purchase totals = $959.38       $1,026.3766   $1,026.37   $1,026.40   $1,026.50