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 $205.50   9.857%   $225.7561   $225.76   $225.75   $225.80  
  Purchase #2 $151.37   9.655%   $165.9848   $165.98   $166.00   $166.00  
  Purchase #3 $53.39   8.497%   $57.9265   $57.93   $57.95   $57.90  
  Purchase #4 $27.40   5.392%   $28.8774   $28.88   $28.90   $28.90  
  Purchase #5 $232.41   4.323%   $242.4571   $242.46   $242.45   $242.50  
  Purchase #6 $143.74   5.330%   $151.4013   $151.40   $151.40   $151.40  
  Purchase #7 $172.28   11.433%   $191.9768   $191.98   $192.00   $192.00  
  7 purchase totals = $986.09       $1,064.3800   $1,064.39   $1,064.45   $1,064.50