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 $63.80   9.363%   $69.7736   $69.77   $69.75   $69.80  
  Purchase #2 $240.63   7.619%   $258.9636   $258.96   $258.95   $259.00  
  Purchase #3 $199.84   6.284%   $212.3979   $212.40   $212.40   $212.40  
  Purchase #4 $218.68   13.854%   $248.9759   $248.98   $249.00   $249.00  
  Purchase #5 $43.36   11.279%   $48.2506   $48.25   $48.25   $48.30  
  Purchase #6 $150.37   12.774%   $169.5783   $169.58   $169.60   $169.60  
  Purchase #7 $239.36   7.743%   $257.8936   $257.89   $257.90   $257.90  
  7 purchase totals = $1,156.04       $1,265.8335   $1,265.83   $1,265.85   $1,266.00