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 $110.92   13.246%   $125.6125   $125.61   $125.60   $125.60  
  Purchase #2 $172.74   11.759%   $193.0525   $193.05   $193.05   $193.10  
  Purchase #3 $145.32   4.169%   $151.3784   $151.38   $151.40   $151.40  
  Purchase #4 $64.62   3.733%   $67.0323   $67.03   $67.05   $67.00  
  Purchase #5 $161.69   11.370%   $180.0742   $180.07   $180.05   $180.10  
  Purchase #6 $218.51   11.425%   $243.4748   $243.47   $243.45   $243.50  
  Purchase #7 $46.96   7.626%   $50.5412   $50.54   $50.55   $50.50  
  7 purchase totals = $920.76       $1,011.1659   $1,011.15   $1,011.15   $1,011.20