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 $51.42   10.117%   $56.6222   $56.62   $56.60   $56.60  
  Purchase #2 $141.33   13.713%   $160.7106   $160.71   $160.70   $160.70  
  Purchase #3 $218.60   6.465%   $232.7325   $232.73   $232.75   $232.70  
  Purchase #4 $81.79   11.688%   $91.3496   $91.35   $91.35   $91.30  
  Purchase #5 $26.94   5.340%   $28.3786   $28.38   $28.40   $28.40  
  Purchase #6 $177.41   8.369%   $192.2574   $192.26   $192.25   $192.30  
  Purchase #7 $94.39   5.834%   $99.8967   $99.90   $99.90   $99.90  
  7 purchase totals = $791.88       $861.9476   $861.95   $861.95   $861.90