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 $54.29   11.158%   $60.3477   $60.35   $60.35   $60.30  
  Purchase #2 $33.62   6.813%   $35.9105   $35.91   $35.90   $35.90  
  Purchase #3 $78.81   11.418%   $87.8085   $87.81   $87.80   $87.80  
  Purchase #4 $222.57   9.195%   $243.0353   $243.04   $243.05   $243.00  
  Purchase #5 $87.94   6.784%   $93.9058   $93.91   $93.90   $93.90  
  Purchase #6 $211.91   4.334%   $221.0942   $221.09   $221.10   $221.10  
  Purchase #7 $223.58   3.709%   $231.8726   $231.87   $231.85   $231.90  
  7 purchase totals = $912.72       $973.9746   $973.98   $973.95   $973.90