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 $195.78   12.313%   $219.8864   $219.89   $219.90   $219.90  
  Purchase #2 $143.55   10.320%   $158.3644   $158.36   $158.35   $158.40  
  Purchase #3 $114.37   7.621%   $123.0861   $123.09   $123.10   $123.10  
  Purchase #4 $196.53   5.602%   $207.5396   $207.54   $207.55   $207.50  
  Purchase #5 $138.39   8.864%   $150.6569   $150.66   $150.65   $150.70  
  Purchase #6 $133.97   9.860%   $147.1794   $147.18   $147.20   $147.20  
  Purchase #7 $23.79   7.702%   $25.6223   $25.62   $25.60   $25.60  
  7 purchase totals = $946.38       $1,032.3351   $1,032.34   $1,032.35   $1,032.40