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 $41.60   6.611%   $44.3502   $44.35   $44.35   $44.40  
  Purchase #2 $127.60   8.668%   $138.6604   $138.66   $138.65   $138.70  
  Purchase #3 $18.45   13.211%   $20.8874   $20.89   $20.90   $20.90  
  Purchase #4 $200.47   13.281%   $227.0944   $227.09   $227.10   $227.10  
  Purchase #5 $26.43   12.268%   $29.6724   $29.67   $29.65   $29.70  
  Purchase #6 $114.86   12.325%   $129.0165   $129.02   $129.00   $129.00  
  Purchase #7 $209.36   12.564%   $235.664   $235.66   $235.65   $235.70  
  7 purchase totals = $738.77       $825.3453   $825.34   $825.30   $825.50