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 $54.62   8.481%   $59.2523   $59.25   $59.25   $59.30  
  Purchase #2 $125.39   10.503%   $138.5597   $138.56   $138.55   $138.60  
  Purchase #3 $129.78   11.817%   $145.1161   $145.12   $145.10   $145.10  
  Purchase #4 $183.41   8.526%   $199.0475   $199.05   $199.05   $199.00  
  Purchase #5 $206.86   10.548%   $228.6796   $228.68   $228.70   $228.70  
  Purchase #6 $241.58   6.739%   $257.8601   $257.86   $257.85   $257.90  
  Purchase #7 $7.65   5.811%   $8.0945   $8.09   $8.10   $8.10  
  7 purchase totals = $949.29       $1,036.6098   $1,036.61   $1,036.60   $1,036.70