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 $65.43   6.644%   $69.7772   $69.78   $69.80   $69.80  
  Purchase #2 $153.42   4.120%   $159.7409   $159.74   $159.75   $159.70  
  Purchase #3 $14.42   11.865%   $16.1309   $16.13   $16.15   $16.10  
  Purchase #4 $214.57   5.444%   $226.2512   $226.25   $226.25   $226.30  
  Purchase #5 $146.80   8.238%   $158.8934   $158.89   $158.90   $158.90  
  Purchase #6 $189.55   7.816%   $204.3652   $204.37   $204.35   $204.40  
  Purchase #7 $79.84   13.737%   $90.8076   $90.81   $90.80   $90.80  
  7 purchase totals = $864.03       $925.9664   $925.97   $926.00   $926.00