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 $212.34   6.699%   $226.5647   $226.56   $226.55   $226.60  
  Purchase #2 $48.63   8.728%   $52.8744   $52.87   $52.85   $52.90  
  Purchase #3 $241.76   11.456%   $269.456   $269.46   $269.45   $269.50  
  Purchase #4 $220.72   12.705%   $248.7625   $248.76   $248.75   $248.80  
  Purchase #5 $228.87   5.277%   $240.9475   $240.95   $240.95   $240.90  
  Purchase #6 $220.65   12.424%   $248.0636   $248.06   $248.05   $248.10  
  Purchase #7 $22.89   7.553%   $24.6189   $24.62   $24.60   $24.60  
  7 purchase totals = $1,195.86       $1,311.2876   $1,311.28   $1,311.20   $1,311.40