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 $146.86   11.566%   $163.8458   $163.85   $163.85   $163.80  
  Purchase #2 $218.95   7.603%   $235.5968   $235.60   $235.60   $235.60  
  Purchase #3 $57.62   4.567%   $60.2515   $60.25   $60.25   $60.30  
  Purchase #4 $247.58   7.716%   $266.6833   $266.68   $266.70   $266.70  
  Purchase #5 $29.31   3.134%   $30.2286   $30.23   $30.25   $30.20  
  Purchase #6 $80.98   8.396%   $87.7791   $87.78   $87.80   $87.80  
  Purchase #7 $20.41   11.373%   $22.7312   $22.73   $22.75   $22.70  
  7 purchase totals = $801.71       $867.1163   $867.12   $867.20   $867.10