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 $158.86   9.571%   $174.0645   $174.06   $174.05   $174.10  
  Purchase #2 $212.52   6.220%   $225.7387   $225.74   $225.75   $225.70  
  Purchase #3 $222.48   4.456%   $232.3937   $232.39   $232.40   $232.40  
  Purchase #4 $11.86   11.873%   $13.2681   $13.27   $13.25   $13.30  
  Purchase #5 $205.98   5.565%   $217.4428   $217.44   $217.45   $217.40  
  Purchase #6 $46.27   3.573%   $47.9232   $47.92   $47.90   $47.90  
  Purchase #7 $60.88   9.762%   $66.8231   $66.82   $66.80   $66.80  
  7 purchase totals = $918.85       $977.6541   $977.64   $977.60   $977.60