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 $95.61   9.698%   $104.8823   $104.88   $104.90   $104.90  
  Purchase #2 $179.97   13.169%   $203.6702   $203.67   $203.65   $203.70  
  Purchase #3 $115.96   3.296%   $119.782   $119.78   $119.80   $119.80  
  Purchase #4 $173.30   4.824%   $181.66   $181.66   $181.65   $181.70  
  Purchase #5 $179.55   5.622%   $189.6443   $189.64   $189.65   $189.60  
  Purchase #6 $74.35   6.444%   $79.1411   $79.14   $79.15   $79.10  
  Purchase #7 $133.87   3.591%   $138.6773   $138.68   $138.70   $138.70  
  7 purchase totals = $952.61       $1,017.4572   $1,017.45   $1,017.50   $1,017.50