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 $220.98   11.577%   $246.5629   $246.56   $246.55   $246.60  
  Purchase #2 $6.42   4.690%   $6.7211   $6.72   $6.70   $6.70  
  Purchase #3 $16.40   6.730%   $17.5037   $17.50   $17.50   $17.50  
  Purchase #4 $195.72   3.193%   $201.9693   $201.97   $201.95   $202.00  
  Purchase #5 $221.62   6.570%   $236.1804   $236.18   $236.20   $236.20  
  Purchase #6 $235.87   6.184%   $250.4562   $250.46   $250.45   $250.50  
  Purchase #7 $130.85   7.611%   $140.809   $140.81   $140.80   $140.80  
  7 purchase totals = $1,027.86       $1,100.2026   $1,100.20   $1,100.15   $1,100.30