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 $39.30   4.258%   $40.9734   $40.97   $40.95   $41.00  
  Purchase #2 $135.75   7.500%   $145.9313   $145.93   $145.95   $145.90  
  Purchase #3 $187.79   7.170%   $201.2545   $201.25   $201.25   $201.30  
  Purchase #4 $23.72   3.317%   $24.5068   $24.51   $24.50   $24.50  
  Purchase #5 $80.25   8.475%   $87.0512   $87.05   $87.05   $87.10  
  Purchase #6 $9.98   6.661%   $10.6448   $10.64   $10.65   $10.60  
  Purchase #7 $61.96   11.398%   $69.0222   $69.02   $69.00   $69.00  
  7 purchase totals = $538.75       $579.3842   $579.37   $579.35   $579.40