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 $181.92   3.551%   $188.38   $188.38   $188.40   $188.40  
  Purchase #2 $89.84   11.143%   $99.8509   $99.85   $99.85   $99.90  
  Purchase #3 $36.66   13.255%   $41.5193   $41.52   $41.50   $41.50  
  Purchase #4 $61.92   12.349%   $69.5665   $69.57   $69.55   $69.60  
  Purchase #5 $217.66   7.599%   $234.2   $234.20   $234.20   $234.20  
  Purchase #6 $246.51   8.705%   $267.9687   $267.97   $267.95   $268.00  
  Purchase #7 $153.37   13.745%   $174.4507   $174.45   $174.45   $174.50  
  7 purchase totals = $987.88       $1,075.9361   $1,075.94   $1,075.90   $1,076.10