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 $60.52   13.778%   $68.8584   $68.86   $68.85   $68.90  
  Purchase #2 $83.61   12.293%   $93.8882   $93.89   $93.90   $93.90  
  Purchase #3 $228.27   13.281%   $258.5865   $258.59   $258.60   $258.60  
  Purchase #4 $189.74   5.111%   $199.4376   $199.44   $199.45   $199.40  
  Purchase #5 $248.51   5.829%   $262.9956   $263.00   $263.00   $263.00  
  Purchase #6 $249.96   13.850%   $284.5795   $284.58   $284.60   $284.60  
  Purchase #7 $228.44   10.856%   $253.2394   $253.24   $253.25   $253.20  
  7 purchase totals = $1,289.05       $1,421.5852   $1,421.60   $1,421.65   $1,421.60