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 $218.70   10.526%   $241.7204   $241.72   $241.70   $241.70  
  Purchase #2 $193.37   9.286%   $211.3263   $211.33   $211.35   $211.30  
  Purchase #3 $114.85   4.494%   $120.0114   $120.01   $120.00   $120.00  
  Purchase #4 $219.50   11.326%   $244.3606   $244.36   $244.35   $244.40  
  Purchase #5 $55.39   8.872%   $60.3042   $60.30   $60.30   $60.30  
  Purchase #6 $18.90   8.661%   $20.5369   $20.54   $20.55   $20.50  
  Purchase #7 $148.35   11.753%   $165.7856   $165.79   $165.80   $165.80  
  7 purchase totals = $969.06       $1,064.0454   $1,064.05   $1,064.05   $1,064.00