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 $151.64   11.112%   $168.4902   $168.49   $168.50   $168.50  
  Purchase #2 $181.70   10.698%   $201.1383   $201.14   $201.15   $201.10  
  Purchase #3 $119.69   11.431%   $133.3718   $133.37   $133.35   $133.40  
  Purchase #4 $203.43   11.302%   $226.4217   $226.42   $226.40   $226.40  
  Purchase #5 $19.58   13.415%   $22.2067   $22.21   $22.20   $22.20  
  Purchase #6 $133.72   3.592%   $138.5232   $138.52   $138.50   $138.50  
  Purchase #7 $179.30   3.748%   $186.0202   $186.02   $186.00   $186.00  
  7 purchase totals = $989.06       $1,076.1721   $1,076.17   $1,076.10   $1,076.10