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 $119.26   11.226%   $132.6481   $132.65   $132.65   $132.60  
  Purchase #2 $95.56   13.130%   $108.107   $108.11   $108.10   $108.10  
  Purchase #3 $83.91   9.367%   $91.7698   $91.77   $91.75   $91.80  
  Purchase #4 $215.52   12.423%   $242.294   $242.29   $242.30   $242.30  
  Purchase #5 $32.43   7.264%   $34.7857   $34.79   $34.80   $34.80  
  Purchase #6 $147.50   12.397%   $165.7856   $165.79   $165.80   $165.80  
  Purchase #7 $7.80   10.291%   $8.6027   $8.60   $8.60   $8.60  
  7 purchase totals = $701.98       $783.9929   $784.00   $784.00   $784.00