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 $118.44   13.427%   $134.3429   $134.34   $134.35   $134.30  
  Purchase #2 $158.87   9.834%   $174.4933   $174.49   $174.50   $174.50  
  Purchase #3 $92.58   4.341%   $96.5989   $96.60   $96.60   $96.60  
  Purchase #4 $102.94   10.279%   $113.5212   $113.52   $113.50   $113.50  
  Purchase #5 $117.79   5.551%   $124.3285   $124.33   $124.35   $124.30  
  Purchase #6 $10.60   3.685%   $10.9906   $10.99   $11.00   $11.00  
  Purchase #7 $219.48   8.650%   $238.465   $238.47   $238.45   $238.50  
  7 purchase totals = $820.70       $892.7404   $892.74   $892.75   $892.70