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 $187.94   12.758%   $211.9174   $211.92   $211.90   $211.90  
  Purchase #2 $157.40   5.242%   $165.6509   $165.65   $165.65   $165.70  
  Purchase #3 $189.27   7.229%   $202.9523   $202.95   $202.95   $203.00  
  Purchase #4 $83.96   13.443%   $95.2467   $95.25   $95.25   $95.20  
  Purchase #5 $226.32   9.258%   $247.2727   $247.27   $247.25   $247.30  
  Purchase #6 $204.75   8.790%   $222.7475   $222.75   $222.75   $222.70  
  Purchase #7 $245.56   9.543%   $268.9938   $268.99   $269.00   $269.00  
  7 purchase totals = $1,295.20       $1,414.7813   $1,414.78   $1,414.75   $1,414.80