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 $116.98   10.251%   $128.9716   $128.97   $128.95   $129.00  
  Purchase #2 $216.59   10.536%   $239.4099   $239.41   $239.40   $239.40  
  Purchase #3 $144.26   6.461%   $153.5806   $153.58   $153.60   $153.60  
  Purchase #4 $67.45   11.720%   $75.3551   $75.36   $75.35   $75.40  
  Purchase #5 $183.38   8.496%   $198.96   $198.96   $198.95   $199.00  
  Purchase #6 $59.36   8.860%   $64.6193   $64.62   $64.60   $64.60  
  Purchase #7 $180.41   11.581%   $201.3033   $201.30   $201.30   $201.30  
  7 purchase totals = $968.43       $1,062.1998   $1,062.20   $1,062.15   $1,062.30