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 $250.84   10.118%   $276.22   $276.22   $276.20   $276.20  
  Purchase #2 $110.41   7.544%   $118.7393   $118.74   $118.75   $118.70  
  Purchase #3 $15.43   12.641%   $17.3805   $17.38   $17.40   $17.40  
  Purchase #4 $55.56   11.286%   $61.8305   $61.83   $61.85   $61.80  
  Purchase #5 $103.40   3.662%   $107.1865   $107.19   $107.20   $107.20  
  Purchase #6 $217.83   9.258%   $237.9967   $238.00   $238.00   $238.00  
  Purchase #7 $184.62   3.315%   $190.7402   $190.74   $190.75   $190.70  
  7 purchase totals = $938.09       $1,010.0937   $1,010.10   $1,010.15   $1,010.00