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 $232.60   6.541%   $247.8144   $247.81   $247.80   $247.80  
  Purchase #2 $90.54   3.471%   $93.6826   $93.68   $93.70   $93.70  
  Purchase #3 $138.97   10.115%   $153.0268   $153.03   $153.05   $153.00  
  Purchase #4 $69.40   10.759%   $76.8667   $76.87   $76.85   $76.90  
  Purchase #5 $14.67   3.756%   $15.221   $15.22   $15.20   $15.20  
  Purchase #6 $77.25   13.816%   $87.9229   $87.92   $87.90   $87.90  
  Purchase #7 $22.52   12.325%   $25.2956   $25.30   $25.30   $25.30  
  7 purchase totals = $645.95       $699.8300   $699.83   $699.80   $699.80