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 $249.46   5.254%   $262.5666   $262.57   $262.55   $262.60  
  Purchase #2 $46.35   12.442%   $52.1169   $52.12   $52.10   $52.10  
  Purchase #3 $235.73   6.724%   $251.5805   $251.58   $251.60   $251.60  
  Purchase #4 $226.39   11.756%   $253.0044   $253.00   $253.00   $253.00  
  Purchase #5 $5.58   5.299%   $5.8757   $5.88   $5.90   $5.90  
  Purchase #6 $138.63   10.413%   $153.0655   $153.07   $153.05   $153.10  
  Purchase #7 $160.84   12.531%   $180.9949   $180.99   $181.00   $181.00  
  7 purchase totals = $1,062.98       $1,159.2045   $1,159.21   $1,159.20   $1,159.30