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 $174.79   5.402%   $184.2322   $184.23   $184.25   $184.20  
  Purchase #2 $145.48   12.490%   $163.6505   $163.65   $163.65   $163.70  
  Purchase #3 $159.31   5.783%   $168.5229   $168.52   $168.50   $168.50  
  Purchase #4 $84.36   12.211%   $94.6612   $94.66   $94.65   $94.70  
  Purchase #5 $248.57   8.825%   $270.5063   $270.51   $270.50   $270.50  
  Purchase #6 $25.51   10.330%   $28.1452   $28.15   $28.15   $28.10  
  Purchase #7 $143.46   5.810%   $151.795   $151.80   $151.80   $151.80  
  7 purchase totals = $981.48       $1,061.5133   $1,061.52   $1,061.50   $1,061.50