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 $224.60   7.650%   $241.7819   $241.78   $241.80   $241.80  
  Purchase #2 $158.70   12.757%   $178.9454   $178.95   $178.95   $178.90  
  Purchase #3 $22.90   6.566%   $24.4036   $24.40   $24.40   $24.40  
  Purchase #4 $166.39   13.771%   $189.3036   $189.30   $189.30   $189.30  
  Purchase #5 $114.56   6.117%   $121.5676   $121.57   $121.55   $121.60  
  Purchase #6 $236.35   6.419%   $251.5213   $251.52   $251.50   $251.50  
  Purchase #7 $39.35   9.402%   $43.0497   $43.05   $43.05   $43.00  
  7 purchase totals = $962.85       $1,050.5731   $1,050.57   $1,050.55   $1,050.50