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 $53.96   10.708%   $59.738   $59.74   $59.75   $59.70  
  Purchase #2 $226.61   6.814%   $242.0512   $242.05   $242.05   $242.10  
  Purchase #3 $138.36   5.474%   $145.9338   $145.93   $145.95   $145.90  
  Purchase #4 $75.71   3.800%   $78.587   $78.59   $78.60   $78.60  
  Purchase #5 $169.75   13.503%   $192.6713   $192.67   $192.65   $192.70  
  Purchase #6 $74.98   6.572%   $79.9077   $79.91   $79.90   $79.90  
  Purchase #7 $218.30   9.621%   $239.3026   $239.30   $239.30   $239.30  
  7 purchase totals = $957.67       $1,038.1916   $1,038.19   $1,038.20   $1,038.20