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 $205.68   11.667%   $229.6767   $229.68   $229.70   $229.70  
  Purchase #2 $118.31   9.121%   $129.1011   $129.10   $129.10   $129.10  
  Purchase #3 $183.69   10.349%   $202.7001   $202.70   $202.70   $202.70  
  Purchase #4 $51.54   11.158%   $57.2908   $57.29   $57.30   $57.30  
  Purchase #5 $205.29   10.152%   $226.131   $226.13   $226.15   $226.10  
  Purchase #6 $70.37   10.401%   $77.6892   $77.69   $77.70   $77.70  
  Purchase #7 $5.81   7.689%   $6.2567   $6.26   $6.25   $6.30  
  7 purchase totals = $840.69       $928.8456   $928.85   $928.90   $928.90