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 $184.36   5.426%   $194.3634   $194.36   $194.35   $194.40  
  Purchase #2 $193.51   12.360%   $217.4278   $217.43   $217.45   $217.40  
  Purchase #3 $43.79   10.493%   $48.3849   $48.38   $48.40   $48.40  
  Purchase #4 $153.35   12.639%   $172.7319   $172.73   $172.75   $172.70  
  Purchase #5 $228.90   13.255%   $259.2407   $259.24   $259.25   $259.20  
  Purchase #6 $235.46   4.273%   $245.5212   $245.52   $245.50   $245.50  
  Purchase #7 $88.99   8.704%   $96.7357   $96.74   $96.75   $96.70  
  7 purchase totals = $1,128.36       $1,234.4056   $1,234.40   $1,234.45   $1,234.30