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 $201.47   8.218%   $218.0268   $218.03   $218.05   $218.00  
  Purchase #2 $152.55   8.718%   $165.8493   $165.85   $165.85   $165.80  
  Purchase #3 $51.49   11.429%   $57.3748   $57.37   $57.35   $57.40  
  Purchase #4 $12.53   11.869%   $14.0172   $14.02   $14.00   $14.00  
  Purchase #5 $243.90   8.779%   $265.312   $265.31   $265.30   $265.30  
  Purchase #6 $188.68   12.223%   $211.7424   $211.74   $211.75   $211.70  
  Purchase #7 $229.25   9.494%   $251.015   $251.02   $251.00   $251.00  
  7 purchase totals = $1,079.87       $1,183.3375   $1,183.34   $1,183.30   $1,183.20