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 $226.25   6.733%   $241.4834   $241.48   $241.50   $241.50  
  Purchase #2 $65.83   11.381%   $73.3221   $73.32   $73.30   $73.30  
  Purchase #3 $85.56   9.407%   $93.6086   $93.61   $93.60   $93.60  
  Purchase #4 $61.80   10.561%   $68.3267   $68.33   $68.35   $68.30  
  Purchase #5 $215.88   12.338%   $242.5153   $242.52   $242.50   $242.50  
  Purchase #6 $174.64   13.835%   $198.8014   $198.80   $198.80   $198.80  
  Purchase #7 $98.50   11.717%   $110.0412   $110.04   $110.05   $110.00  
  7 purchase totals = $928.46       $1,028.0987   $1,028.10   $1,028.10   $1,028.00