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 $158.41   5.360%   $166.9008   $166.90   $166.90   $166.90  
  Purchase #2 $125.89   9.297%   $137.594   $137.59   $137.60   $137.60  
  Purchase #3 $38.45   8.619%   $41.764   $41.76   $41.75   $41.80  
  Purchase #4 $246.34   8.507%   $267.2961   $267.30   $267.30   $267.30  
  Purchase #5 $229.52   3.236%   $236.9473   $236.95   $236.95   $236.90  
  Purchase #6 $16.43   4.171%   $17.1153   $17.12   $17.10   $17.10  
  Purchase #7 $123.59   12.705%   $139.2921   $139.29   $139.30   $139.30  
  7 purchase totals = $938.63       $1,006.9096   $1,006.91   $1,006.90   $1,006.90