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 $38.26   7.227%   $41.0251   $41.03   $41.05   $41.00  
  Purchase #2 $222.66   12.529%   $250.5571   $250.56   $250.55   $250.60  
  Purchase #3 $195.55   11.844%   $218.7109   $218.71   $218.70   $218.70  
  Purchase #4 $159.42   8.595%   $173.1221   $173.12   $173.10   $173.10  
  Purchase #5 $5.88   11.654%   $6.5653   $6.57   $6.55   $6.60  
  Purchase #6 $200.61   3.589%   $207.8099   $207.81   $207.80   $207.80  
  Purchase #7 $150.95   9.395%   $165.1318   $165.13   $165.15   $165.10  
  7 purchase totals = $973.33       $1,062.9222   $1,062.93   $1,062.90   $1,062.90