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 $238.37   13.697%   $271.0195   $271.02   $271.00   $271.00  
  Purchase #2 $102.99   4.587%   $107.7142   $107.71   $107.70   $107.70  
  Purchase #3 $87.65   3.500%   $90.7178   $90.72   $90.70   $90.70  
  Purchase #4 $116.46   10.660%   $128.8746   $128.87   $128.85   $128.90  
  Purchase #5 $225.78   6.401%   $240.2322   $240.23   $240.25   $240.20  
  Purchase #6 $41.73   4.526%   $43.6187   $43.62   $43.60   $43.60  
  Purchase #7 $169.28   6.633%   $180.5083   $180.51   $180.50   $180.50  
  7 purchase totals = $982.26       $1,062.6853   $1,062.68   $1,062.60   $1,062.60