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 $111.94   11.370%   $124.6676   $124.67   $124.65   $124.70  
  Purchase #2 $45.94   3.250%   $47.4331   $47.43   $47.45   $47.40  
  Purchase #3 $55.37   4.838%   $58.0488   $58.05   $58.05   $58.00  
  Purchase #4 $180.66   7.161%   $193.5971   $193.60   $193.60   $193.60  
  Purchase #5 $112.49   11.415%   $125.3307   $125.33   $125.35   $125.30  
  Purchase #6 $180.36   6.396%   $191.8958   $191.90   $191.90   $191.90  
  Purchase #7 $228.79   11.415%   $254.9064   $254.91   $254.90   $254.90  
  7 purchase totals = $915.55       $995.8795   $995.89   $995.90   $995.80