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 $63.52   9.709%   $69.6872   $69.69   $69.70   $69.70  
  Purchase #2 $93.72   5.480%   $98.8559   $98.86   $98.85   $98.90  
  Purchase #3 $116.46   13.869%   $132.6118   $132.61   $132.60   $132.60  
  Purchase #4 $171.76   9.262%   $187.6684   $187.67   $187.65   $187.70  
  Purchase #5 $63.36   5.776%   $67.0197   $67.02   $67.00   $67.00  
  Purchase #6 $204.86   10.605%   $226.5854   $226.59   $226.60   $226.60  
  Purchase #7 $74.80   7.367%   $80.3105   $80.31   $80.30   $80.30  
  7 purchase totals = $788.48       $862.7389   $862.75   $862.70   $862.80