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 $57.86   12.387%   $65.0271   $65.03   $65.05   $65.00  
  Purchase #2 $107.43   9.343%   $117.4672   $117.47   $117.45   $117.50  
  Purchase #3 $58.88   10.299%   $64.9441   $64.94   $64.95   $64.90  
  Purchase #4 $214.81   9.388%   $234.9764   $234.98   $235.00   $235.00  
  Purchase #5 $143.83   5.575%   $151.8485   $151.85   $151.85   $151.80  
  Purchase #6 $211.90   10.411%   $233.9609   $233.96   $233.95   $234.00  
  Purchase #7 $38.53   13.427%   $43.7034   $43.70   $43.70   $43.70  
  7 purchase totals = $833.24       $911.9276   $911.93   $911.95   $911.90