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 $202.29   6.556%   $215.5521   $215.55   $215.55   $215.60  
  Purchase #2 $102.72   3.243%   $106.0512   $106.05   $106.05   $106.10  
  Purchase #3 $5.58   11.152%   $6.2023   $6.20   $6.20   $6.20  
  Purchase #4 $144.40   7.337%   $154.9946   $154.99   $155.00   $155.00  
  Purchase #5 $241.85   10.712%   $267.757   $267.76   $267.75   $267.80  
  Purchase #6 $11.91   3.112%   $12.2806   $12.28   $12.30   $12.30  
  Purchase #7 $231.52   9.828%   $254.2738   $254.27   $254.25   $254.30  
  7 purchase totals = $940.27       $1,017.1116   $1,017.10   $1,017.10   $1,017.30