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 $163.52   6.528%   $174.1946   $174.19   $174.20   $174.20  
  Purchase #2 $53.44   11.266%   $59.4606   $59.46   $59.45   $59.50  
  Purchase #3 $41.30   12.365%   $46.4067   $46.41   $46.40   $46.40  
  Purchase #4 $51.34   12.302%   $57.6558   $57.66   $57.65   $57.70  
  Purchase #5 $43.38   5.349%   $45.7004   $45.70   $45.70   $45.70  
  Purchase #6 $216.85   4.211%   $225.9816   $225.98   $226.00   $226.00  
  Purchase #7 $206.48   12.596%   $232.4882   $232.49   $232.50   $232.50  
  7 purchase totals = $776.31       $841.8879   $841.89   $841.90   $842.00