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 $148.64   13.701%   $169.0052   $169.01   $169.00   $169.00  
  Purchase #2 $216.93   7.809%   $233.8701   $233.87   $233.85   $233.90  
  Purchase #3 $77.95   10.682%   $86.2766   $86.28   $86.30   $86.30  
  Purchase #4 $79.26   11.585%   $88.4423   $88.44   $88.45   $88.40  
  Purchase #5 $96.82   13.269%   $109.667   $109.67   $109.65   $109.70  
  Purchase #6 $245.46   4.337%   $256.1056   $256.11   $256.10   $256.10  
  Purchase #7 $64.59   5.315%   $68.023   $68.02   $68.00   $68.00  
  7 purchase totals = $929.65       $1,011.3898   $1,011.40   $1,011.35   $1,011.40