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 $96.78   10.187%   $106.639   $106.64   $106.65   $106.60  
  Purchase #2 $115.95   7.163%   $124.2555   $124.26   $124.25   $124.30  
  Purchase #3 $149.97   10.213%   $165.2864   $165.29   $165.30   $165.30  
  Purchase #4 $185.96   11.483%   $207.3138   $207.31   $207.30   $207.30  
  Purchase #5 $165.62   11.103%   $184.0088   $184.01   $184.00   $184.00  
  Purchase #6 $155.43   5.575%   $164.0952   $164.10   $164.10   $164.10  
  Purchase #7 $73.76   10.785%   $81.715   $81.72   $81.70   $81.70  
  7 purchase totals = $943.47       $1,033.3137   $1,033.33   $1,033.30   $1,033.30