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 $62.81   13.600%   $71.3522   $71.35   $71.35   $71.40  
  Purchase #2 $163.37   11.764%   $182.5888   $182.59   $182.60   $182.60  
  Purchase #3 $137.65   9.553%   $150.7997   $150.80   $150.80   $150.80  
  Purchase #4 $161.57   4.626%   $169.0442   $169.04   $169.05   $169.00  
  Purchase #5 $91.75   6.324%   $97.5523   $97.55   $97.55   $97.60  
  Purchase #6 $158.51   8.700%   $172.3004   $172.30   $172.30   $172.30  
  Purchase #7 $217.80   3.768%   $226.0067   $226.01   $226.00   $226.00  
  7 purchase totals = $993.46       $1,069.6443   $1,069.64   $1,069.65   $1,069.70