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 $236.81   5.788%   $250.5166   $250.52   $250.50   $250.50  
  Purchase #2 $65.72   6.193%   $69.79   $69.79   $69.80   $69.80  
  Purchase #3 $212.75   5.760%   $225.0044   $225.00   $225.00   $225.00  
  Purchase #4 $114.96   12.118%   $128.8909   $128.89   $128.90   $128.90  
  Purchase #5 $101.89   5.613%   $107.6091   $107.61   $107.60   $107.60  
  Purchase #6 $165.85   8.773%   $180.4   $180.40   $180.40   $180.40  
  Purchase #7 $229.59   9.640%   $251.7225   $251.72   $251.70   $251.70  
  7 purchase totals = $1,127.57       $1,213.9335   $1,213.93   $1,213.90   $1,213.90