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 $68.90   12.140%   $77.2645   $77.26   $77.25   $77.30  
  Purchase #2 $195.78   9.136%   $213.6665   $213.67   $213.65   $213.70  
  Purchase #3 $228.26   3.163%   $235.4799   $235.48   $235.50   $235.50  
  Purchase #4 $14.52   9.728%   $15.9325   $15.93   $15.95   $15.90  
  Purchase #5 $224.37   10.864%   $248.7456   $248.75   $248.75   $248.70  
  Purchase #6 $94.46   10.791%   $104.6532   $104.65   $104.65   $104.70  
  Purchase #7 $157.95   13.503%   $179.278   $179.28   $179.30   $179.30  
  7 purchase totals = $984.24       $1,075.0202   $1,075.02   $1,075.05   $1,075.10