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 $154.96   7.249%   $166.1931   $166.19   $166.20   $166.20  
  Purchase #2 $234.79   4.274%   $244.8249   $244.82   $244.80   $244.80  
  Purchase #3 $117.83   5.742%   $124.5958   $124.60   $124.60   $124.60  
  Purchase #4 $207.42   13.455%   $235.3284   $235.33   $235.35   $235.30  
  Purchase #5 $229.84   11.344%   $255.913   $255.91   $255.90   $255.90  
  Purchase #6 $218.50   12.801%   $246.4702   $246.47   $246.45   $246.50  
  Purchase #7 $234.95   8.399%   $254.6835   $254.68   $254.70   $254.70  
  7 purchase totals = $1,398.29       $1,528.0089   $1,528.00   $1,528.00   $1,528.00