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 $212.76   12.314%   $238.9593   $238.96   $238.95   $239.00  
  Purchase #2 $86.66   4.192%   $90.2928   $90.29   $90.30   $90.30  
  Purchase #3 $213.46   9.624%   $234.0034   $234.00   $234.00   $234.00  
  Purchase #4 $186.41   8.697%   $202.6221   $202.62   $202.60   $202.60  
  Purchase #5 $65.60   8.707%   $71.3118   $71.31   $71.30   $71.30  
  Purchase #6 $139.43   4.395%   $145.5579   $145.56   $145.55   $145.60  
  Purchase #7 $27.99   12.839%   $31.5836   $31.58   $31.60   $31.60  
  7 purchase totals = $932.31       $1,014.3309   $1,014.32   $1,014.30   $1,014.40