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 $59.68   13.131%   $67.5166   $67.52   $67.50   $67.50  
  Purchase #2 $22.73   11.809%   $25.4142   $25.41   $25.40   $25.40  
  Purchase #3 $144.40   9.844%   $158.6147   $158.61   $158.60   $158.60  
  Purchase #4 $145.83   7.178%   $156.2977   $156.30   $156.30   $156.30  
  Purchase #5 $58.86   6.581%   $62.7336   $62.73   $62.75   $62.70  
  Purchase #6 $230.92   11.619%   $257.7506   $257.75   $257.75   $257.80  
  Purchase #7 $133.69   10.597%   $147.8571   $147.86   $147.85   $147.90  
  7 purchase totals = $796.11       $876.1845   $876.18   $876.15   $876.20