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 $66.38   10.572%   $73.3977   $73.40   $73.40   $73.40  
  Purchase #2 $112.95   10.592%   $124.9137   $124.91   $124.90   $124.90  
  Purchase #3 $179.65   12.554%   $202.2033   $202.20   $202.20   $202.20  
  Purchase #4 $134.88   11.646%   $150.5881   $150.59   $150.60   $150.60  
  Purchase #5 $221.62   12.127%   $248.4959   $248.50   $248.50   $248.50  
  Purchase #6 $66.25   4.755%   $69.4002   $69.40   $69.40   $69.40  
  Purchase #7 $68.42   6.873%   $73.1225   $73.12   $73.10   $73.10  
  7 purchase totals = $850.15       $942.1214   $942.12   $942.10   $942.10