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 $213.53   9.620%   $234.0716   $234.07   $234.05   $234.10  
  Purchase #2 $203.42   12.189%   $228.2149   $228.21   $228.20   $228.20  
  Purchase #3 $165.32   12.730%   $186.3652   $186.37   $186.35   $186.40  
  Purchase #4 $10.47   12.124%   $11.7394   $11.74   $11.75   $11.70  
  Purchase #5 $150.53   11.455%   $167.7732   $167.77   $167.75   $167.80  
  Purchase #6 $106.89   6.571%   $113.9137   $113.91   $113.90   $113.90  
  Purchase #7 $113.55   11.501%   $126.6094   $126.61   $126.60   $126.60  
  7 purchase totals = $963.71       $1,068.6874   $1,068.68   $1,068.60   $1,068.70