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 $138.75   8.860%   $151.0433   $151.04   $151.05   $151.00  
  Purchase #2 $115.52   5.632%   $122.0261   $122.03   $122.05   $122.00  
  Purchase #3 $35.67   8.579%   $38.7301   $38.73   $38.75   $38.70  
  Purchase #4 $244.87   9.732%   $268.7007   $268.70   $268.70   $268.70  
  Purchase #5 $248.75   6.791%   $265.6426   $265.64   $265.65   $265.60  
  Purchase #6 $72.78   5.785%   $76.9903   $76.99   $77.00   $77.00  
  Purchase #7 $98.68   12.277%   $110.7949   $110.79   $110.80   $110.80  
  7 purchase totals = $955.02       $1,033.9280   $1,033.92   $1,034.00   $1,033.80