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 $211.53   5.564%   $223.2995   $223.30   $223.30   $223.30  
  Purchase #2 $218.61   6.171%   $232.1004   $232.10   $232.10   $232.10  
  Purchase #3 $116.92   3.765%   $121.322   $121.32   $121.30   $121.30  
  Purchase #4 $38.70   7.787%   $41.7136   $41.71   $41.70   $41.70  
  Purchase #5 $113.84   5.780%   $120.42   $120.42   $120.40   $120.40  
  Purchase #6 $126.52   8.416%   $137.1679   $137.17   $137.15   $137.20  
  Purchase #7 $71.77   3.826%   $74.5159   $74.52   $74.50   $74.50  
  7 purchase totals = $897.89       $950.5393   $950.54   $950.45   $950.50