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 $15.69   9.192%   $17.1322   $17.13   $17.15   $17.10  
  Purchase #2 $161.58   7.473%   $173.6549   $173.65   $173.65   $173.70  
  Purchase #3 $15.52   7.829%   $16.7351   $16.74   $16.75   $16.70  
  Purchase #4 $160.53   4.551%   $167.8357   $167.84   $167.85   $167.80  
  Purchase #5 $237.41   10.559%   $262.4781   $262.48   $262.50   $262.50  
  Purchase #6 $41.37   7.234%   $44.3627   $44.36   $44.35   $44.40  
  Purchase #7 $136.98   5.370%   $144.3358   $144.34   $144.35   $144.30  
  7 purchase totals = $769.08       $826.5345   $826.54   $826.60   $826.50