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 $162.77   10.374%   $179.6558   $179.66   $179.65   $179.70  
  Purchase #2 $83.65   11.339%   $93.1351   $93.14   $93.15   $93.10  
  Purchase #3 $148.53   8.656%   $161.3868   $161.39   $161.40   $161.40  
  Purchase #4 $245.29   9.783%   $269.2867   $269.29   $269.30   $269.30  
  Purchase #5 $119.89   13.658%   $136.2646   $136.26   $136.25   $136.30  
  Purchase #6 $63.52   4.547%   $66.4083   $66.41   $66.40   $66.40  
  Purchase #7 $46.43   5.579%   $49.0203   $49.02   $49.00   $49.00  
  7 purchase totals = $870.08       $955.1576   $955.17   $955.15   $955.20