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 $172.95   8.127%   $187.0056   $187.01   $187.00   $187.00  
  Purchase #2 $173.92   10.647%   $192.4373   $192.44   $192.45   $192.40  
  Purchase #3 $241.84   5.758%   $255.7651   $255.77   $255.75   $255.80  
  Purchase #4 $35.31   4.557%   $36.9191   $36.92   $36.90   $36.90  
  Purchase #5 $231.96   6.745%   $247.6057   $247.61   $247.60   $247.60  
  Purchase #6 $23.57   11.559%   $26.2945   $26.29   $26.30   $26.30  
  Purchase #7 $130.53   4.806%   $136.8033   $136.80   $136.80   $136.80  
  7 purchase totals = $1,010.08       $1,082.8306   $1,082.84   $1,082.80   $1,082.80