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 $167.83   5.107%   $176.4011   $176.40   $176.40   $176.40  
  Purchase #2 $147.96   3.711%   $153.4508   $153.45   $153.45   $153.50  
  Purchase #3 $26.60   5.593%   $28.0877   $28.09   $28.10   $28.10  
  Purchase #4 $182.56   13.208%   $206.6725   $206.67   $206.65   $206.70  
  Purchase #5 $149.62   13.405%   $169.6766   $169.68   $169.70   $169.70  
  Purchase #6 $150.51   11.821%   $168.3018   $168.30   $168.30   $168.30  
  Purchase #7 $174.73   6.243%   $185.6384   $185.64   $185.65   $185.60  
  7 purchase totals = $999.81       $1,088.2289   $1,088.23   $1,088.25   $1,088.30