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 $169.63   10.398%   $187.2681   $187.27   $187.25   $187.30  
  Purchase #2 $156.84   13.268%   $177.6495   $177.65   $177.65   $177.60  
  Purchase #3 $98.54   12.213%   $110.5747   $110.57   $110.55   $110.60  
  Purchase #4 $93.67   6.335%   $99.604   $99.60   $99.60   $99.60  
  Purchase #5 $146.89   4.864%   $154.0347   $154.03   $154.05   $154.00  
  Purchase #6 $69.97   5.322%   $73.6938   $73.69   $73.70   $73.70  
  Purchase #7 $160.67   8.253%   $173.9301   $173.93   $173.95   $173.90  
  7 purchase totals = $896.21       $976.7549   $976.74   $976.75   $976.70