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 $66.50   6.597%   $70.887   $70.89   $70.90   $70.90  
  Purchase #2 $106.66   13.123%   $120.657   $120.66   $120.65   $120.70  
  Purchase #3 $156.93   3.275%   $162.0695   $162.07   $162.05   $162.10  
  Purchase #4 $183.51   7.820%   $197.8605   $197.86   $197.85   $197.90  
  Purchase #5 $167.82   6.632%   $178.9498   $178.95   $178.95   $178.90  
  Purchase #6 $54.46   8.223%   $58.9382   $58.94   $58.95   $58.90  
  Purchase #7 $145.46   13.833%   $165.5815   $165.58   $165.60   $165.60  
  7 purchase totals = $881.34       $954.9435   $954.95   $954.95   $955.00