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 $208.69   12.611%   $235.0079   $235.01   $235.00   $235.00  
  Purchase #2 $106.27   13.582%   $120.7036   $120.70   $120.70   $120.70  
  Purchase #3 $131.50   7.130%   $140.876   $140.88   $140.90   $140.90  
  Purchase #4 $100.25   9.791%   $110.0655   $110.07   $110.05   $110.10  
  Purchase #5 $124.70   5.294%   $131.3016   $131.30   $131.30   $131.30  
  Purchase #6 $181.43   10.345%   $200.1989   $200.20   $200.20   $200.20  
  Purchase #7 $54.75   13.525%   $62.1549   $62.15   $62.15   $62.20  
  7 purchase totals = $907.59       $1,000.3084   $1,000.31   $1,000.30   $1,000.40