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 $177.81   10.422%   $196.3414   $196.34   $196.35   $196.30  
  Purchase #2 $232.43   3.529%   $240.6325   $240.63   $240.65   $240.60  
  Purchase #3 $26.86   9.759%   $29.4813   $29.48   $29.50   $29.50  
  Purchase #4 $128.32   5.198%   $134.9901   $134.99   $135.00   $135.00  
  Purchase #5 $27.83   6.220%   $29.561   $29.56   $29.55   $29.60  
  Purchase #6 $195.94   8.332%   $212.2657   $212.27   $212.25   $212.30  
  Purchase #7 $205.76   9.320%   $224.9368   $224.94   $224.95   $224.90  
  7 purchase totals = $994.95       $1,068.2088   $1,068.21   $1,068.25   $1,068.20