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 $212.72   13.372%   $241.1649   $241.16   $241.15   $241.20  
  Purchase #2 $98.83   10.657%   $109.3623   $109.36   $109.35   $109.40  
  Purchase #3 $20.76   13.327%   $23.5267   $23.53   $23.55   $23.50  
  Purchase #4 $75.44   12.432%   $84.8187   $84.82   $84.80   $84.80  
  Purchase #5 $212.99   8.258%   $230.5787   $230.58   $230.60   $230.60  
  Purchase #6 $50.91   13.142%   $57.6006   $57.60   $57.60   $57.60  
  Purchase #7 $190.50   6.829%   $203.5092   $203.51   $203.50   $203.50  
  7 purchase totals = $862.15       $950.5611   $950.56   $950.55   $950.60