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 $76.57   7.791%   $82.5356   $82.54   $82.55   $82.50  
  Purchase #2 $191.33   4.262%   $199.4845   $199.48   $199.50   $199.50  
  Purchase #3 $148.89   4.276%   $155.2565   $155.26   $155.25   $155.30  
  Purchase #4 $66.89   7.148%   $71.6713   $71.67   $71.65   $71.70  
  Purchase #5 $149.65   10.305%   $165.0714   $165.07   $165.05   $165.10  
  Purchase #6 $245.92   9.585%   $269.4914   $269.49   $269.50   $269.50  
  Purchase #7 $195.78   11.348%   $217.9971   $218.00   $218.00   $218.00  
  7 purchase totals = $1,075.03       $1,161.5078   $1,161.51   $1,161.50   $1,161.60